I'm punching above my weight

All my friends, and even work colleagues that I don't know too well, tell me I'm punching above my weight when I show them pictures of my girlfriend. This is something I know myself though, and she makes me a better person because she is so amazing.

These are friends from school and university... from back when I was very immature & a bit chubbier - my diet was awful, I drank and went out most nights but, saying that, I've always been a good hearted person. Since then I've been training and working on my personality - my physique and overall appearance has improved, along with my personality (I'm a lot more mature). I also get a lot more attention now.

I do feel that if I knew my current gf at university she wouldn't have gone for me then. But I can see why she likes me now because of the drastic changes I've made, and I'm also very confident with her whereas back then I wouldn't have known what to do with such a pretty lady.

So when my friends say this, is it possible they are taking my past in to account too? Or is it really just as I am at this current moment in time?

What the hell does "punching above my weight" even mean?

Like my girlfriend is too good for me