Can your age deter you from becoming pregnant easily?

I've been thinking lately that i may be infertile, there have been many occasions where me and my fiance could have become pregnant, but it hasn't happened. I was wandering if a person's age can make it easier or harder on getting pregnant, say a 15/16 year old compared to someone in their 20's. Could it be harder for the younger ones to become pregnant, but you see quite a number of young parents now. I was just curious and wandered as im having trouble getting pregnant. Please help, i would like to understand more fully about my situation. Thankyou.