Three of my Whites are about 3 to 3 1/2 inches from nose to butt. One is only about 2 1/4 inch and is a slow grower. Not sure on age but I bought them when they were about 1 to 1 1/2 inches and that was in late September I believe. They grow pretty quickly.
The enclosure does look big and that is mostly because of the outer wood casing which one side adds at least 6 inches to the side for wiring and controlers (which I only have switches in now).
As for the shell, I baked it but the silicone I have won't stick well.
I eventually get it to work and its vacation week for me so plenty of time to have some fun.