Will and Ryan are right. Unfortunately, a lot of young riders dream of becoming a famous rider but it is really hard. If your parents have good relations in the equestrian milieu, it can be easier. But it costs a lot of money and take all your time. You have to be ready for this way of life!
I am not gonna lie, it is hard. You have to train a lot. Find stables where you can ride prestigious horses, do a lot of competitions, try to have a lot of relations. You also need to have enough money to afford everything as it is a very irregular profession, you can win money in a show and then nothing during 2 months!!