I haven’t played most of these, but I will gladly add an endorsement to the early Harry Potter games. They often only tangentially related to the movies, but they had some awesome mechanics, and played into the full story really well.
While it never got much past the concept phase, I think it would be fun to play a circle of stars druid as a magical girl. I was thinking this ancient elven man who learned a bit of the druidic magics of his people, but was always more fascinated with the stars. One day he connected with a group of gnomes who invented a flying machine that could take them to the moon, and immediately signed up for the trip. When he got there, he discovered a moon goddess that had been trapped there. They hit it off famously, he offered to help free her, and she turned him into a knight of sorts, giving him the transformation ability. When he transforms, he turns into this young, bubbly, vivacious eleven woman with crazy armor and the standard anime oversized weapon that is based on which form he transformed into. She still has all the same memories, ideas and goals, but with a completely different personality. It would be pretty entertaining.
The oldest system I have would be the NES. My brother received it sometime before I was born. I’m just holding onto it for him, though - it doesn’t get played right now. I actually intend to clean it all up and retrobright it before sending it back to him… eventually… The oldest system I have that still gets occasional use would be my Gameboy Color, which I received, with Pokemon Red, for Christmas when I was 8 or 9. Unfortunately, I need to find a better plastic polish, to take some light scratches out of the lens, and until I do, it will remain disassembled… I’ve also been contemplating using the board for a complete boxypixel overhaul, but there’s something about still having my full original GBC that I’m having a problem getting over…