You've had 3 BFPs from 4 IVF - that's pretty awesome in my books! I know 2 of them could not stay with you, but you're still doing better than I did TTC#1 (1 BFP from 5 cycles) and I was 32-34 during those cycles.

While you're still producing eggs, it's still possible.

I'll be lucky if I don't hit menopause before 42, so we're all different. All you can do is keep going so long as it's right for you and stop when it's no longer right to continue. No-one can tell you when it's time to throw in the towel, it's something you and your partner have to work out for yourselves.