How’s his weight? Has the vet said anything about him being over or under?
How much does he eat now for pellets? Does he eat quickly?
Mine are 9 and 9.5+ years and are still free fed. (Though I’ll clarify they are not flemish giants. Rupert is the biggest at around 9 pounds-he’s big but not giant
)
They don’t devour their pellets (in fact I buy four types to encourage them to eat them!) and eat plenty of hay so -so far for me, I haven’t had to ever stop free feeding. I know not everyone can do that, but they are grazers so I prefer if they can eat whenever they feel the need. They don’t get excited about pellets, they could care less-because they’ve always had them available.
So I don’t know that there is a fixed age-though generally most people stop free feeding 6-12 months. I would use your vets opinion (of his weight/health) as a guide, and also how he eats his pellets-does he eat a ton or does he eat some and eat his hay really well. Does he scoff them down quickly? If so you may want to switch to portions sooner. Does he eat his hay well? If he’s not skipping hay for pellets, you could likely continue free feeding for the time being.