Is there a legal limit on what age you can put your kids up for adoption?

[hatredisnotavalue]

Warning RANT

I got an 18 soon to be 19 yo girl and a 17 yo boy.
The diva just got off a stellar performance in the school musical and isn't talking to any of us. In fact when her brother asked for the car keys to drive home yesterday, she told him she didn't have them even though she had driven the car to the school for softball practice.
So he called me for a ride home because she wouldn't give him the keys. I walked into softball practice and embarrassed her by asking for the keys to the other car, gave them to the son, and told him to drive the other car home.

Son is getting ready for SATs, daughter isn't speaking to him and she could really help him with the deal. Daughter also didn't get into the college she had hoped for although she doesn't know it yet. She isn't speaking to any of us, but, boy oh boy, would I love to belt her with the bad news right now. But I won't because that is juvenile. She had hoped to get into an Ivy League school, but didn't although she has gotten offers from some great school with lots of scholarship money.
I am getting so tired of being a parent. Sigh...Should I tell her she didn't get into the school she wanted just to knock her off her pedestal? She is going to find out soon enough, but at this point she needs the wind knocked out of her sails to bring her down a notch, I don't know.... what do you think?