We were, yes, & in the same month, apparently! We grow more alike by the day, eh?
I didn't find 18 to be a big deal whatsoever, myself. I spent my teenage years getting into clubs, buying smokes/alcohol, etc, between that & the things I was up to, I had a full dose of "adulthood" long before the law said I should.
21 didn't really land for the same reasons. Now, at 26, I still feel like a teenager in many respects. Not so much for petty high school sorts of reasons, but mainly due to my desire to just have fun, be a bit careless, get by thanks to music, & so on. At the same time, the fact I'm NOT one is way more evident than ever before, as I watch people around me getting married, having kids, etc. I also feel like sh*t, but it's probably more to do with health problems than it is aging. I've definitely had a lot of realizations about what it means to get older, though. Things my parents told me as a kid finally make sense, but not for the better.
Some wisdom, is a burden.
It is true that once you reach a certain age, time seems to increase doubly, perhaps moreso. I googled that phenomena some time back, & they say its because you generally create less memories, & sorta run out of milestones for a while, which would otherwise create mental checkpoints. Stating it so vaguely it may seem a bit odd, but look it up, there are a lot of points which make perfect sense of it. Scary, in a way, really.