What's your mental age?

We've heard many people use this term... sometimes in a derogatory manner. But the other day VR and I were discussing how we pretty much considered ourselves to be the age we were when we set foot on Cincinnati to begin our Masters degree. And it's been 4 years since then. And because of that, all of a sudden when my real age dawns on me, I feel disproportionately old. And it's unsettling. I think the reason behind this is that leaving India (or one's own country) and going to the US for a degree all by oneself was a big deal. And that was the last life-altering change that took place in our lives. Even including marriage. The responsibilities multiplied when we first had to live alone, cook alone and manage bills, accounts, shopping and what not alone all amongst trying to keep the grades high and those all-nighters for assignments, midterms and finals. And we each mastered our individualities, developed our personalities and the metamorphosis from dependent child to independent adult was fast completed. Which is why even after something as huge as a wedding, I still feel the same age as I was when I first went to the US. And all of a sudden, we're reading about these actresses and models, who are 1986 born and even later. And for one fleeting second, the thought crosses the mind - is it legal for them to work, even? And suddenly you realize it's 2008 and they're 22 and yes that's legal. And that time's going faster than you've accounted for. Hell... practically everyone you know is married or on the verge of even including the boys (men is more appropriate) of your age. Many of your classmates are having kids and it's obvious that we're all very very grown up. I guess it helps everyone to be at that comfortable age that they can relate to. For me, it's 23. What's yours?