So if I understand correctly, your choices are party with the 18 year olds, celebrate invisibly with the older crowd or remain alone?
I see why the last two options suck, but what wrong with the first?
I'll be 31 in a few short months and celebrated my niece's 18th with her 2 weeks ago.
Then again, I wasn't the only one in my age group there, the mid twenties - thirties, were keeping an eye on things while having a blast ourselves. I would've preferred to be home before 4am though, because I had work the next day.