Issue with Age?

[GSAS082612]

So, as I have mentioned before previously, I am in a poly-amorous relationship with a married couple. They have been married for a little over a year. I have known my girlfriend and boyfriend since I was 15. I am now 18. The biggest issue I am getting is the age. They for one, share one daughter and a son on the way, with a possible newborn on my part. (Trying for a baby) Anyways, the issue everyone suggests I bring up is age, she is 21, and he is 34. I know not many are supportive, but what is your opinion. Please no smack talk on my boyfriends or girlfriends age, or telling me I am too young. Life is too short to live it right. I am 18 and I understand that this could quite possibly be a mistake but in fact, it could not be. I love him, I love her. Point Blank. But I am curious with how many othe poly-relationships have an age gap so wide.