There seems to be a lot wrong with this relationship.
I would question the intentions, mental health, and maturity of a 33 year old man who wants a relationship with a teenager.
I would question any person who tells their SO they want to take a step like meeting the parents, but then delays it for seven years.
Mostly, I would question any person who is trying to make their SO aware of possible drawbacks to their relationship. It seems like he’s trying to tell you the age difference is too much. You didn’t say you had a conversation about it once or twice. You said he “keeps” bringing it up. Yet another red flag.
edit: By “question” the maturity, etc of a man in a relationship with a teenager, I mean just that. I know it can work and be healthy, but I would still have concerns.