Answer : No Just Disney. Families are their bread and butter, and they should want to encourage the continued family bonding experience ........ especially when the "kids" are over 17. Keep the "adult" kids coming with their families and they will more than likely keep coming with their own families when they have kids........which should be very soon given the "adult" kids age.
Few other hotels in the world are as much of a destination as they are at WDW. They can and do set there own standards.
In a perfect world for families staying at WDW, they can up the adult age to a more common age that "adult" kids may have moved out of the house. 18 y/o is rare for kids to move out these days. How about making the adult extra charge 25 y/o. Just a thought.
Also as much as age on a picture ID is non-debatable............ well so is the persons name

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Believe me ........... Disney knows that our 19 y/o daughter is our daughter. They know everything about us for the past 20 years !
I am not debating the extra adult charge, nor am I refusing to pay it, I just wish WDW would recognise that if your very young adult "kid" who is really too young to stay on their own and needs to stay in the "family" room ........ there shouldn't be an extra charge for it.
Oh well.........nothing any of us can do about it !
We are going to WDW in a month and WILL be paying the extra "adult" $25. fee for out Disney born and raised daughter.
Maybe Disney wants us to charge our daughter the extra $25. per night to recoup our money

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Syndrome