Firstly by showing you can be a responsible carer, do some research and show him you know what you're doing.
Do jobs to earn some money to set up the enclosure lighting etc yourself, if he's not keen on you keeping sit down and have a talk about why you want it and what your willing to do to pay for things it will need.
they are great pets and I'm sure if you can show him it's not a phase he'll cave eventually : p