...that some people born in 1990 are adults now?
Sure, if you were born then maybe it's not such a shock. If you were graduating from high school round about then, then it seems a wee bit of a shock that people you consider babies (because you left when they were babies) are themselves about to finish high school.
I feel old now. :-)
I think time appears to pass more quickly the older you get. This makes some sense to me, since when you were, say, four years old, one year was 25% of all of the time you had ever known (and probably 100% as long as all of the time you could remember). By the time you get to 30, a year is just 3% of all the time you have ever known. If you manage to get to 100, it's only 1%, so maybe it tends to slow down. After all, the derivative of 1/x is -1/(x*x).