Well, there is the societal expectation that in order to "grow up" a man must stop spending time with his friends and/or on his hobbies and "settle down". There is no such expectation/pressure on women.
There is a lot of pressure on women to have children, though, and having kids drastically changes how, when, and with whom you socialize.
To elaborate, in case you don't have kids: for the first several months, you're likely exhausted and don't even want to socialize. If you do, you're still limited due to time - young children just sleep and eat, and you're bound to their schedule. If you're exclusively breastfeeding, you can't drive an hour out to see a two hour movie with your friends, because your kiddo's feed is going to fall within that timespan.
Once they get older, you can go out again, but you're not going to necessarily be doing the same things you wanted to earlier. Being woken up hungover by a screaming baby at 5am is terrible, so you're going to cut down your social drinking. Going camping on the weekend is more difficult, too - you're leaving your partner in the lurch. Spur of the moment plans are difficult, too - you're still tied to your kid's schedule, and there are places where it is difficult to take a small child. ("You wanna go rock climbing?" "Yes, but...")
We all, regardless of gender, face different types of pressures from outside. Women are often seen (and mystified) through motherhood, and men through stoic toiling. Women are supposed to be the emotional ones, and men hard and logical and impervious to emotions. You see it all the time in various forums when people comment on a sad article, with the "I'm not crying, I'm cutting onions schtick." A lot of this comes down to old gender roles born out of a confusing soup of evolution, Abrahamic social norms, and history. It's not just the men facing social pressures, it's everybody in the society.
> Well, there is the societal expectation that in order to "grow up" a man must stop spending time with his friends and/or on his hobbies and "settle down".
I'm not sure I've ever encountered that expectation. I'm in my 30's and have four or five close friends I spend regular time with and a load of other 'mates' that I see every now and then.
To elaborate, in case you don't have kids: for the first several months, you're likely exhausted and don't even want to socialize. If you do, you're still limited due to time - young children just sleep and eat, and you're bound to their schedule. If you're exclusively breastfeeding, you can't drive an hour out to see a two hour movie with your friends, because your kiddo's feed is going to fall within that timespan.
Once they get older, you can go out again, but you're not going to necessarily be doing the same things you wanted to earlier. Being woken up hungover by a screaming baby at 5am is terrible, so you're going to cut down your social drinking. Going camping on the weekend is more difficult, too - you're leaving your partner in the lurch. Spur of the moment plans are difficult, too - you're still tied to your kid's schedule, and there are places where it is difficult to take a small child. ("You wanna go rock climbing?" "Yes, but...")