Dear Andy!
Looking a way lot younger has more worst effect than looking older than your real age.
The first thing you have to face is the questionable look and attitude of everyone in high school. Everyone including most teachers are thinking and asking "Hey kid!, shouldn't you be in your own grade rather than roaming around this section?"
The second thing is that all the girls say "He's a cute little kid!" instead of "He's a cool or handsome guy!"
After college you can't drive a car without the cops telling you to "pull over" at each square and again the long session of convincing them that you are not a minor etc. You don't know the attitude of the police of Pakistan; they have an expert method (with a good beating session) of convincing an elephant that he is a deer! Unless you are wearing a racing helmet while driving a car!
Furthermore when you walk in for an interview for a job; the whole office bursts into laughter after seeing that you are holding a degree or two and think that this is some kind of a joke!
But! the most important thing is that you won't find a suitable match to marry. All the girls of the same age look a lot older than us and they reject us by saying "You look like my little bratty brother!"
Jokes apart, you can cope with all this, but it really is annoying to be a lot younger than your age!