For someone playing -.4 years? Like 100'.
But in all seriousness, and this is coming from someone that is 16, how young you are is not really an excuse anymore unless you are like <13. It's all about EXPERIENCE. Just keep working hard and you'll get there at the same pace the adults do, and watch out for the adults that throw tantrums when you do
.
If you want an example though, I can (consistently) throw about 300' backhand and 300 forehand