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