My TB also fits this description. I got him as a coming 6yo. He’s a very slow to mature type physically (characteristic of his sire from what I’ve been told). We spent most of his 6yo year correcting physical issues (hooves, ulcers, bodywork). 7yo year was starting to take consistent lessons, some trail riding, a few schooling outings to take in the sights.
2023 was his 8yo year and we spent most of it on dressage bootcamp. He felt mentally and physically ready to actually do a dressage show in April, a long state park trail ride in July, and try our first foray into the hunter/jumper show ring in December.
Could a pro or a different rider have done this faster? Probably. Was there anything to gain by rushing? Nope. We both needed the time to develop a partnership and for him to develop the physical strength to handle what was being asked.
Long story short - it’s your horse and your timeline. Anyone pressuring you to do more or faster can feel free to do that with their own horse, not yours. You’ll know when you and your horse are ready to progress.