I would say it's ok for gaming. Probably getting close to the end of its life cycle though. If it were mine I'd leave it on iOS 8. Put 9 on there and it'll probably crawl.
It can work for more casual games. Plus, I'd only do it if you could get it for cheap. Check online, but AFAIK, a new one at 32 GB should be less than $75. Otherwise, pay an extra $100 more even for an Ipad mini2 According to an Ars Technica review for the Ipad (regular) 2, going to ios8 to ios9 is worth it. It'll still be relatively lousy performance, but ios9 was made to be better performing. If anything, it's leaving ios7 you should be concerned about assuming that's an option. If the Ipad mini 1 you get has something before that, then may as well update to ios9 (not that you can choose which version at this point).