Well, a computer is an essential tool in many jobs and even university and college nowadays so I guess you can get some good use from it and tell your dad it will be beneficial for your future and then, alongside that, you can also fulfil your gaming needs.

Usually the more you spend on the computer, the longer it will be usable for (obviously there will be diminish returns the more you pay since it's not linear) be it 7 or even 10 years down the line, especially if it's a desktop where you can go around and upgrade some parts every, say 3 years, to keep up with the technological advancements.

If you feel like it, you can even buy the parts yourself and build it. Can even ask your dad to help. Can be a very fun experience. I once did the same (not with my dad but with my cousin, point still stands) and it was pretty interesting.