I have been a SAHM for the last 9 years. At first it was VERY tough, as like you, I had been working since I was 16. (I was 35 when I had our first child) Even tho I loved being home with our son I went stir crazy for a while. I had a job - not really a career - but I was around people all the time and I loved the social life.

I worked in documentation so I had to get information from a variety of people so I knew a lot of my co-workers. I wrote for the company newsletter sometime, volunteered at the blood drives, kids holiday party, and other things - when I was at home I missed all that. I also didn't like "play groups" - since I didn't like other Mom's just because they had kids. I missed having friends that I had other things in common with other than having children. (Everyone I knew went back to work after having kids)
We went through secondary infertility problems which was a nightmare in itself. When DD was born I was 39 and more settled in a routine. Now the kids are 5 & 9 and it's MUCH easier for us to have me at home. DD is in pre-school and DS in in 3rd grade. I am able to drive them to school and go in for different events. I have also volunteered in DS's class and will continue that in the fall when DD goes to kindergarten. I can also get the homework (nightmare sometimes) done before DH gets home.
While I loved the baby stage with my children, part of why I wanted to be a SAHM was to be able to participate in my children's education. I know their teachers, I know their friends, I know some of the other Mom's - to me that is a good thing.
I would NOT recommend being a SAHM to everyone. One of my good friends thinks I'm nuts to stay home!

It's a choice only you can make. I don't make judgement on women who work outside the home - or those who don't. I am fortuante that financially right now I don't have to work. We had our kids later in life so I worked many years and we saved $$$. I'm not sure what will happen in the future. I also have my parents (78 & 83) living nearby and I am so thankful that I get to spend a lot of time with them. (Spent most of the day with them today with DD..)
But one thing I do notice is that I tend to answer threads with long posts since I don't always get a lot of adult interaction during the day and I use my DIS time for that.
I hope that things work out for you the way you want!!
Jill