If you deadlifted 340 at age 14, you should be at 500-600 by now.
Nop in fact I don't deadlift anymore I hate the feeling I get in my back.
When I first start training I was doing weightlifting at school so for 1 year all I did was squat, deads, clean and jerk, snatch (fucked my shoulder doing snatch)
right now I think I could deadlift around 475 for one rep, I'll try it next back workout.
A friend of mine who is really overweight did 220 kg the first time he deadlifted ! at 16 years old. He weighted 315 at the time if I remember well.
I think that was really impressive, now he is much stronger. I haven't seen him lately but I heard he is doing great in weightlifting