Me, My Love, and His Nanny?...wow.?

okay so me and my significant other have been together almost 4 years and planning on getting married this coming up summer or next year after we graduate. the thing is his nanny loves me like her own granddaughter. he tells me she loves me everytime im there and she absolutly loves us together. but a problem is that even though she looks great for her age she isnt in the best health. if we lost her id feel like i lost my own nanny. so the other day she made a comment saying that she hopes shes still living by the time we have grandkids. and she was almost in tears. she wonderful and i dont want that to come true. but we are 17 and yes we both have a wonderful future that we have financially prepared and basically live together already for 3 years but i dont know if we should have a baby yet.i know your thinking were too young to be thinking about it but we are more prepared than alot of full grown adults are.my question is about a baby?we are in love and will do anythng for each other