I don't want to belabor the basic, but you do know that while your eggs are all you will ever have and will age, his sperm is always created fresh all his life, right? So him being 40 is not anywhere near as serious an issue reproductively as it would be if you were 40.
I agree with AnnieBrooke. I'd look into it more before doing something like freezing his sperm just yet. All of these procdures are outrageously expensive unless insurance will cover it, and you are still young.
Even if you use frozen sperm, you don't need to go through the entire IVF process unless there is something wrong with your unassisted fertility. You could either get pregnant the natural way, if it is in only a few years, or you could use his frozen sperm in a regular cycle of yours (without bothering with IVF). Please look into the entire question. Freezing sperm for a man of only 40 who is not facing any known threats to his fertility is pretty costly and bothersome.