Hi,
I have a very pretty mum too, although no surgery in this case, she's just naturally young-looking and really knows how to dress. She gets attention from younger guys (Not as young as me thankfully), even though she tries to avoid it. It's a source of amusement for us both.
Bear in mind that guys your age may well just be joking when they comment i.e., they mean she does look fantastic for her age, but it doesn't mean they actually fancy her or want to date her. You may be just low on self-esteem at the moment and you're taking their comments too seriously as a result.
Take comfort in the fact that even without surgery, you're going to look great at 40 too, and that you'll be able to talk to your mum about fashion etc. and get sensible opinions and advice.