15 (nearly 16) girl, want to ride dirt bikes no experience pushbikes or dirtbikes, too old?HELP?

please help, i have recently been influenced by travis pastrana and i think that job would be awesome, unfortunatley my elder brother has said im too old and pathetic to do it. i dont know where to begin, i havent so much as seen my push bike in 5 years but i really want to be a dirt biker. any suggestions or people that you know have started late and become amazing?