Parents are also to blame. Too many let their children take up valuable space for years past their expulsion date because it's easier than telling them to grow up and move out.
More than one set of parents has moved house into a dwelling that does not have enough space for adult children to free themselves from the burden of perpetual caregiving.
Economics plays a part, too. If someone can't afford to leave the family home to set up one of their own, he or she is trapped in an environment where they have always been treated like a child.
Consequently, serious long-term relationships are not entered into until later in life and a cycle of immaturity is established, because trying to have a serious relationship used to be an effective way to make yourself grow up.
Marketing to men seldom emphasises brand values of maturity, common sense and stability. Instead, they are invited to attend product shows such as Big Boys Toys. And why not? After all, they are big boys and you can never have too many toys, can you?
Television aimed at men glorifies permanent adolescent behaviour, frequently involving groups of grown men - Hamish and Andy, the cast of Top Gear, Jono and Ben - engaging in the sort of pranks and antics you might have expected them to have grown out of. It's worth noting that when Jono and Ben inveigled their way on to Graham Norton's Red Chair, they did so wearing school uniforms.
For entertainment, men have a stream of movies based on comic books in which women feature barely, if at all. They no longer have to confine video game playing to their living rooms but, thanks to smartphones, can carry them everywhere they go and play them whenever they want.
It is accepted they will dress in garments that present them as pre-pubescent neuters, such as onesies and overalls, as though they are characters in a Maurice Sendak picture book. Many never don a pair of long pants, but wear shorts year-round.
They even eat like children - encouraged to indulge in comfort food and enjoy the wide range of snacks and sweets on offer in the supermarkets. That can't be good for them.
But in general, as a lot of women will tell you, the real problem with men not growing up is that they don't grow up.