Stuck

My husband is turning 37 this year, I’m 31. We have 2 kids together (6 and 2 year old). He has a 12 year old from a previous marriage. I would love to have a 3rd kid with him but he has given me an ultimatum of either conceiving this year in a few months or it’s not going to happen at all. He feels like he’s too old to have any more kids and idk what to do.