I am new to having a RES pet. I currently have a RES around the age of 2 years and is 5" long. He is in a 55 gallon tank set up currently, that I plan on upgrading once settled into a bigger place. Bought him about a month ago and I enjoy having him as a pet. Now I really want to get a RES hatchling. Would it be okay to put them into the same tank as the older one? If not, could he be raised while young in a 20 gallon tank and eventually put it in the larger tank with the other RES?
Any input that is helpful would be much appreciated.

Thank you!