Here's my take on this:
1) My partner and I have very different education levels. But that's not important to me, because I love him for the person that he is. His, or my, level of education doesn't change that. Now you have to decide whether your partner's education level is important to you. Having dealbreakers is a valid personal choice, I won't police that in other people, but I think you have to be able to live with those dealbreakers and the consequences that they might have for the kind of people you potentially close yourself off to in life.
2) However, I find it interesting that you mention not only that you're at university, but that you're at a Russell Group university. This to me might be an indicator that you value the status of the education more than the discipline itself. Ask yourself, if he was studying at a non-Russell Group university (as I did, for the record), would you also be thinking that you are at "different stages in life". This part, more than any, is what would make you cross the line into being the A in my opinion. And what about other factors? What if he'd gone to university but dropped out, or not graduated with honours, or (God forbid) gotten a 2:2? I think you need to really consider the way you value education yourself, because honestly, if any of those things apply, then maybe you're the problem.
TLDR: If their level of education is a quality you personally value in a partner, then that's valid and you're NTA. If the status of that education, and where it comes from or how it's "ranked", is what matters, then you're the A. In my opinion.