The shedding is normal, he has probably just never had enough dryness in his shell to shed properly, just look out for any rot underneath the shells.
If he's only been fed protein it's hard to get them to eat anything else. The grow accustom to a great taste and low nutrition.. Trying to feed them strongly scented things is a good way to change thins up. They like shrimp and tuna which has both vitamin D and nutrition but of course is also protein. Could try some dandelion leaves, I hear they like that...