I think that this thread is really building up the potential to get a bit nasty, and that makes me sad!
To the OP- I think that part of the reason that you are getting some very terse responses at this point can be partially attributed to you (unintentionally, I am sure!) with holding information about the details of your tip....namely- that you would be paying the bill for this trip. Had you shared that initially-
'hey- I don't have my own kids, but I ADORE my nephew and I was going to take him when he turns 5, but now I'm running in the Princess Marathon and my sister is campaigning to bring him this time. I would still be paying for this, and I'm just not sure if that's the best way to spend my money when there are so many other things like a college fund, etc. Can those of you who have chosen to wait to take your kids a bit longer share how and why you made that decision? I know that most people who already have taken their younger kids will vigorously defend that decision and that's great if it works for them, but I'm most interested in hearing from people who chose to wait- do you regret waiting now, or do you think it was the right choice?'
I think had you taken this approach you would have gotten a lot more helpful responses and far fewer critical ones. Your tone put a lot of people on the defensive, and by leaving out the fact that you were expected to pay for the trip really did leave the impression that you were looking for reasons/ways to talk your sister out of bringing her son. Your money means you get to make the rules, obviously. I don't think that you having worked at Disney honestly matters that much, although I'm sure it's probably given you a lot to think about

.
My daughter will be 2 months shy of 5 when we go in December and it will be her first trip....but had I been able to go financially, I think I would have taken her at 3. But my son, who is now 12- I NEVER would have taken him that young...they are very different children. DD is very easy to please and doesn't need a lot of coaxing and does well in busy places. DS was very timid and shy and afraid of his shadow and got hugely clingy when we were in crowds, etc. So I would say that a large part of this depends on the particular child. My DD also remembers things that happened when she was under 2- and talks about them with startling clarity. My son's first trip was when he was 5 1/2 and he barely remembers most of it. But he also can't find his shoes 5 minutes after he takes them off. Very, very different kids

. I am almost positive that Ella will remember this trip forever.
You are very right that you don't have to shell out several thousands of dollars to show love and that the simplest things that cost nothing except our time and affection. The problem is that when you walk onto a board of mostly mothers and take a tone that sounds like you're lecturing us and telling us something we don't know- people get their back up pretty quickly. Vacations are a personal thing- if you're the kind of person who will make Disney a once or possibly twice in a childhood experience- then it makes the most sense for Auntie to wait till the kids are old enough to make the most of it.
But bear in mind that since you don't have children (for whatever reasons- no assumptions there), that some of the things that you witness that look miserable to you (waiting in lines, carrying a passed out child, dealing with the crankies, etc)....for those of us who live with our children daily, those are all just such a part of our everyday lives and we don't even think twice about it. I have to deal with most of the things you mentioned on a trip to the grocery store, or the beach down the street. Life with small kids comes with a lot of strings attached. We internalize it and live it and it's just all part of the deal. Even though to a non-parent it might look like we are making things hard(er) on ourselves. And I think that is mostly what folks mean when they say that since you don't parent daily, you might not have the same perspective or opinion as those of us who do. That said- I think that entire can of worms is secondary to the real issue.
When the parents foot the bill, they get to decide what age they take their kids and that's just how it goes. I don't agree with a lot of things I see people dropping money on when it comes to kids. But a Disney vacation isn't necessarily one of them. Though my son doesn't remember most of his first trip...I REMEMBER. I remember sitting on the curb with him at (what was then) MGM and seeing his face when that parade came down the street and when Snow White remembered him from the day before at the MK. *I* remember watching him believe with all the innocence of a child. And you know what? He is now a big, STINKY, more-hairy-every-day 12 year old who googled 'b-o-o-b-s' the other day. And I wouldn't trade those memories for ANYTHING. NOTHING. Did I lose my temper on that trip once or twice? Probably. Did my (then) husband and I have a squabble? Undoubtedly. Do I remember that? Not at all. I remember the look on Brendan's face when he saw the lights of winter at Epcot, and how friggin' adorable he looked in his Mickey Ears with a big old lipstick print from Snow White on his cheek. It will bring me comfort when I am sitting home waiting for him to get back home when he's out too late and the lipstick is from some girl I haven't even met yet. And whether he remembers it or not, it's all part of the life we made together. Parents are allowed to get something out of this deal, too. And that is who you are asking. You aren't asking a bunch of aunts/uncles/godparents/family friends/generous benefactors. You are asking a bunch of parents. And that's just how most of us feel.
The ironic thing is, that as a first time parent, had I spent a lot of time talking with (very well-meaning) folks who have the opinion you do, I probably would have been swayed and opted to not have taken him on that trip, even as a kindergartner- I might have decided to wait a couple more years. And a couple years later- I was in the middle of the most horrible divorce, and a huge medical crisis, and had lost my job and was literally almost on welfare. That trip never would have happened. But he still would have kept right on growing.
I guess my point is that life stops for no one. You *hope* you can take him when he's five. If you're still here, and he's still here, and the money's still there, etc, etc,. Goals and logic are both invaluable things to have in life- don't get me wrong...but there's a beautiful Mama on this very board who lost her 2 year old in a car accident just a couple weeks after they got back from his first time at WDW, and she clings to and cherishes those memories and I can promise you she doesn't regret taking him.
So just- you know- let your heart have some say in the matter, too, and not just your head. Your head is obviously a very good one, and I applaud you for being practical and I think it's obvious you love your nephew (and your sister)...but sometimes, money is only money, and though a deposit to his college fund will definitely be a generous and welcomed gift- time spent with a loving family (anywhere, not just at WDW) can't be bought at any price.
If you're looking for people to tell you it's ok to feel the way you do and it's fine that you decided not to pay for his trip now- it's OK. It really is. It's also OK that some of us would take our kids to Disney every month if we could. You might think that's a foolish way to spend our money. We might think that you're a little *too* practical minded. So what? I've got enough blisters from walking in my own shoes, I don't pretend to know what yours feel like. What I feel that has been lacking in your posts, is that same respect for others who don't agree with you. I think it started badly, and now you feel defensive and attacked (and some posts have been pretty nasty), and it's all just snowballing.
Whatever decision you end up making, I'm sure that your nephew will still love and adore you, and vice versa- and that's the most important thing of all.
I need to get off this board and go make some memories with my DD now

. Right here at home
Rebecca