Some single men may find that marriage and child rearing are not possible due to age or financial reasons. The question then becomes, what is left if you remove marriage/child rearing from your life?
In my opinion, it leaves only work and hobbies. Giving up love, devoting oneself to work, earning a reasonable income, and putting that money into hobbies is, I think, the way of life for the average single man.
It would be great if they could fall in love, but as they get older, women are no longer interested in them. Also, sexual desire will gradually decrease. When that happens, the only thing they can do is to spend time on their work and hobbies. The way of life of a middle-aged single woman may be the same as that of a single man.
If you are really lonely, one way is to become friends with them. Even if you are not sexually attracted to them, having women you can be friends with will help ease the loneliness of being single.