Most guys will start to bald or recede in their hairline in their 20s. I'm in my mid 20s and I've noticed my hairline recede over the last 5 years. In my photos when I'm 18/19 I do not have gaps near my temples, now I have gaps and the hair above my eyebrows is starting to thin. I'm more of a pretty boy than a masculine man so if I lose my hair I lose the majority of my looks/appeal. I have very nice thick voluminous curly hair that even the ladies would be jealous of.
Even if you want to marry a younger woman, most of us will either be bald or have massive foreheads in our 30s or 40s meaning it's unlikely these younger girls will find us attractive. Hair is life, even handsome men look a lot better with hair compared to being bald, jude law is the perfect example of this, there is a reason why most male celebrities will get hair transplants and other treatments done to keep their hairline, their careers depend on their looks. You would think with modern technology we would have a cure for MPB but I guess not.