iPhone 4 is my oldest, and it can't do jack. It has trouble even loading Tin Man games. But I am keeping it around because I'll be damned if I sell it (it was my first). Best Buy will buy it for like $4.
I have everything since 3GS on the iPhone side and iPad mini and newer. I keep these devices to test on since the simulator isn't always good enough. So you could say I game on them haha
I have an iPod 3 and it can run anything which is available for its OS version.(iOS 5) it runs dead space , mutant mudds and even clash of clans without a problem .
My oldest is tied between an iPod 4 and the original iPad, and I never use either one anymore. The iPad is amazingly heavy compared to my new iPad.
i have a 4s and a 5 sitting about 5 feet from me, family / friends always end up buying off my old ipads so my air 2 and the wife's air 1 are as old as i go currently for tablets.
I have an Ipod Touch 5. Was going to get an IpT6, but upon learning it still had the same 4" screen... No. The screen was a requirement for me, even if the rest of the specs received a boost. I have an Ipad Air that I use to distribute battery usage between the 2 devices since the IpT5 is more than 2 years old at this point. When the IpT5 can't hold a charge, I'll have to decide to give up iOS cold turkey, see if an IpT7 is out with a larger screen, if I can get an Iph6+ ("+" as in beyond, not the "plus" model), or just do gaming on my Ipad Air (of which I need to find out how to transfer game saves from IpT5 running ios7 onto there.
The oldest device I have is the iPod Touch 2nd gen. and I guess you can somewhat consider the iPad Mini 1st gen. as a old device as well.