Originally Posted by pigtaru

Ok, in an anime, I think that's fine. Because it's new real. But in real life, a 16 year old dating a 21 year old can be tricky. Not to say that it can't be done or it shouldn't be done, but it's tricky.

Both people would have to be mentally at the same level. Usually, dating here is OK, but relationship wise, I'm not too sure about that. 16 year olds, most of the time, need time to grow, mentally. And as the younger person grows older, they begin to change. So by the time they are 21, they might not be the same person who fell in love with the 21 year old to start with. I would advice against it in real world scenarios.

To sum it up:

Anime 16&21 = OK
Anime 16&Whatever = OK
Real World 16&21 = I wouldn't do it.
Real World 21-Whatever = Fine by me.