Tempo 146 is quite fast, and if I remember right you were like 14 or so so keep it up!!

I myself think now that tempo 208-216 is hard but I can manage to play 16:ths at that tempo (chromatic) but hey, I'm 2 years older than you and when I was in your age I bet I couldn't have managed even with the tempo 120. :)

I bet that when you are as old as I am now you will play something like 250.. Have fun practising, btw, you got Petrucci's Rock Discipline, the chromatic exercises are great training for speed and such..