If you want "smaller" turtles, then look at map turtles. You could house a few of them in a 55 gal for life with no problems. But, as with any aquarium animal/fish, you should give them as much room as you can afford to.
If you get into sliders or cooters, than they will get larger and need a lot more room down the road. Good thing about (most) turtles is that they grow relatively slowly compared to fish, so there is time to prepare and upgrade as needed.
If you get into sliders or cooters, than they will get larger and need a lot more room down the road. Good thing about (most) turtles is that they grow relatively slowly compared to fish, so there is time to prepare and upgrade as needed.