I’m worried for him in many ways as we’ve only been able to give him information we’re allowed to give hums he doesn’t know the full picture
This really jumped out at me. I’m not sure what you mean when you say you’re only allowed to give him certain information? Who has said you can’t tell him all of the information you have about his birth family and his early years?
Unless there are very specific safeguarding concerns, it’s so important he knows everything you do, at a time and in a way her can process. Even if there are safeguarding concerns, there are ways to talk to him about his early years, his birth family and his adoption, and it’s important for him that someone does that. I’m sorry, but you’ve been very badly advised on that.
Life story work can be a therapeutic process, a specific piece of work or can be age appropriate discussions that happen throughout the child’s life where time is given to help them understand their history and to help them make sense if it. The later life letter is part of that but really by the time he gets that, he should know everything it contains, by which I mean there should be no surprises. I think you’re right to be concerned that at 7 he would have very limited understanding of his life story, have you been talking to him about his life over the years or was it left that he knew and there were things you couldn’t tell him? Do you know what he thinks happened that he came to be adopted?
It may be that he has a natural curiosity, especially if there’s information you’ve been told you can give him. He’ll want to fill the gaps and contact with his birth family is one way of doing that. I’d make sure that as far as possible (ie within everything you know) that there aren’t any surprises for him because that would be awful for him.
It may be worth looking for a therapist or SW who can do therapeutic life story work with him, especially if there are parts of his story he doesn’t know yet. It’s not for them to fill the gaps (that’s between you and him), but will be able to help him process all you need to tell him. You can still access post adoption support even though he’s older, I’d be asking them for access to life story work.
He may still want contact with his birth family, but at least he’ll go into it knowing the full picture.