When i was 12 years old i wanted to start karting. Ive always enjoyed racing and so i asked my mum (my brother had a kart, he was 21), "Can i get a kart?"
She said No, too expensive, i have to earn it myself. Of course, I'm 12, i cant get a job and buy a kart THEN keep it maintained.
I'm 17 now and been saving, I'm going to get a kart next year and start racing. Ive saved enough to maintain the kart for a long time (meaning race costs, tires, spare parts etc).
In the end, i have earnt it all on my own, i feel big even though i haven't started racing in a league yet, but at the same time, starting at 12 can get you somewhere... starting at 18, unlikely.. prove me wrong.
So IMO, as long as you got the opportunity to get there, parents, friends, whoever, you've gotten there and should take full advantage of it.