I am just turning 15 and have a crf 100, really want to race, and know people who race. Am I too old?

Hey i'm just turning 15, am pretty comfortable with my crf 100, know people who race, have been to a track, and really want to. I am also 5-11 and between 130-140 pounds. Do you think I am too old to start racing? I plan on getting a race bike too, i want to win but know it wouldnt want to happen for a long time but just love to ride. If you think i can, what size do you think i should get and what bike. BTW i cant afford an $8,000 bike but am going to sell mine.