How difficult is it to learn to ride a dirt bike?

I'm thinking about saving up for a dirt bike...I'm 17 and never ridden one. I know I'm expecting to pay a good 2-5 grand for a used one. I've rode a regular bicycle all my life, so I think that could help, I also have a four wheeler so that might help learning throttle or something. What would you say the most difficult or learning to ride a dirt bike is? If it's balance, I think I got it pretty down pact. I know I may be thinking too far ahead again, but I like to go big. How difficult is it to land big jumps compared to a regular mountain bike? Any information for a beginner would be helpful....