Trying to get pregnant

So my boyfriend is 58 and im 24 and ive been with him for 3 years and love him alot. At one point we were trying to conceive but it just wasnt happening for us. In the 3 years we've been together we havent used protection and he cums in me everytime we have sex. Could something be wrong? Why am i not getting pregnant? I have a 5 year old little boy and 3 year old little girl(not my boyfriends though from a prior relationship).