1. By the time you're 50, he is gonna be 80
There are no issues with dating an older man. But think about it. If you have kids with him, you're gonna be ready to run outside with the kids and partake in their physically and time consuming activities. The older husband will probably want to go to bed or lounge around at home. It will take a toll.
2. Different hobbies/interests
There is no surprise that you may have different tastes in music genre, hobbies, and what you consider to be fun. Maybe you enjoy going out and drinking, and he enjoys staying at home playing backgammon? All things to consider.
3. Gap in sexual appetite
It isn't really a surprise that as we get older we may lose our sex drive. Whether it is old age or simply the inability to perform at a certain level- sex is of 90% importance when it isn't present in a relationship.