Honestly, he'll do fine on 60g to 70g rats every 7 to 10 days, and he'll still skip meals.
If you want to see what he actually needs start small and track his weight. Feed him a weaned rat every week (45g) for a few months. See what his weight does. If you think it's too small, go to a small rat (60g to 70g). Do that for a few months, track his weight and see what it does.
You'll be surprised just how little they need to grow and be healthy compared to what we usually tend to think they need.