Others have already mentioned that the character is only one year away from the "normal" lower bound for starting age; with a difference that small, I wouldn't be inclined to say that it makes any real difference.
If you really, really want to make the character's young age have a mechanical impact, then I could maybe see imposing a general -1 penalty on skill checks: the character hasn't quite learned enough about the world to apply learned knowledge completely just yet. But I'd only impose that penalty until he reaches Level 2, because at that point he should have enough practical experience to counteract the effects of his age. Alternatively, you could work the character's sixteenth birthday into the plot and remove the penalty then.