Had my first child at 28 years old and planning to have 1-2 more. Not ready to get pregnant again though (my daughter just turned 1 a month ago). At what age will infertility become a possible concern of mine?

I remember that on my genetics class, the professor said that quality of eggs decrease by age 30. Quality further decreases as you grow older than that. In my personal observation, infertility becomes a pressing concern by age 40. I think you're still on the right track though :)