Charting you temp and watching your CM would help you recognise the return of fertility.

My periods took about 18 mths to return after each baby (I continued BFing through pregnancy, no worries). My sister fell pregnant first egg (so no periods, and bfing, about 18 mths after baby). I know of woman whos periods returned sooner, and other later...so it is very hard to say when it will be for you. But being aware of your CM can help alert you....or you could just enjoy each other, and later nature take it's course! Good chance you will achieve this before 40.

Have Fun