I would suggest you keep moving. There are many reasons 40 year old men date 25 year old women...and none of them are healthy.
I was that 25 year old woman, and I did marry a 40 year old man...with 4 kids. Frigging nightmare. These chicken hawk older men are immature and difficult people. And they don't get better with age. Guaranteed that you will pass his emotional maturity fairly quickly and you will be wondering why the hell he is so emotionally stunted. Any emotionally healthy 40 year old man should be looking for a woman more his own age, with whom he has a lot more in common.