Manga sometimes mentions this "old man smell." I really don't think guys in their 30s and 40s smell. Maybe older men do because they probably shower less. I don't know.
Old people smell is an actual thing though, which can be reduced with the usual good diet, hygiene, and all that, but it still is a thing that affects us all, known as the "nonenal smell", which starts at around 40 years old.
Japanese people are especially susceptible to it because they're extremely obsessed with being odorless, which leads them to have sensitive noses. Funny enough, this is one of the reasons why Japanese people often avoid being near foreigners in places like trains—our perfumes, or even deodorants, can overwhelm their noses like chemical bombs.