I know you feel geared-up for a monitor, but have you thought about how much long-term commitment is involved? At 13, the next few years of your life are going to be very important to your future, such as if you decide to move out for an apprenticeship, college, or get a job away from your parents house and have to get your own place. Getting a monitor lizard will prevent a lot of that, they're not the most low-maintenance pets, and not something most parents will look after for you if you have stuff to do.
If any of these scenarios worry you, I'd try and find something smaller, and less demanding. Don't kid yourself that options such as rehoming it or selling it are possible, because large monitors are notoriously difficult to get rid of once they get past the 1ft size.
At 13, you probably feel 100% committed to getting a monitor, but things do change. See it almost like a career choice - you're going to serious limit certain opportunities, not to mention it will severely dent any money you earn over the years. Talk it through with your dad, see how much responsibility he's willing to have over it should a tricky situation arise in the future. Your plans for it need to be future-proof, but if you can figure that out, then go for it.
Best,
Paul