I would say it depends on where they are relative to their training. If they're on the right pace for their age, then it's fine. You can always use a salary calc to see what their salaries will be next year.
Also remember that you're buying a guy that's almost a year older, so don't overpay for a 19 year old, when he's really almost a 20 year old at this point.
That's my opinion on the topic. It all depends on their training progress/cost.