Although I am probably a good deal older than your father, I think that I can speak to this.
It is important to find and to have something of depth that you can continue to appreciate and learn from and about long-term, and music has always been one of the most profound forms of art. For me, at about your age, that was Jimi Hendrix and the Mothers of Invention, along with an entire generation of music just coming into bloom that led me down a path that has remained vital (although waxing and waning along the way to some degree) to this day, and taking me far beyond the realm of rock music.
A man in "middle age" with the responsibility of a family (and who knows what other pressures) needs something of his own for a refuge that is personally and privately fulfilling. There is no better escape from the pressures of life than losing oneself in interesting music, in my opinion, and probably in his. You should not begrudge him that - after all, he is providing for you.
Having said that, though, it is very inconsiderate of him to bother you with something that you don't like. The simple solution is for one of you to get a good set of headphones, and/or for lower volume from him when you need quiet for yourself.
I recommend that you go to him with a proposal for something from you in exchange for a computer. Usually that would be grades or chores, but it could be whatever is best for you both. And build it yourself - if you can find an outdated computer free or cheap you might be able to upgrade it piece-by-piece until you have something pretty good. That is likely how your father assembled his stereo, at least in the beginning. My son and I did that as a project and went through upgrade cycles a couple of times a year for several years.
