...or at least don't work after a certain age or for total loners perhaps.
There are a lot of such tips being thrown here when someone loner asks about increasing chance of meeting someone and maybe even having new friends , such as the overused typical "join a social club", "join a Meetup" , "join a cooking class" ..... they all revolve around joining X.
In my experience, those very rarely work for forming new friendships, let alone relationships - these only make you have new temporary acquaintances - who will all disappear after you finish/stop the activity/class.
For example I 've been in extensive 15 months programming courses, the guys were approachable , we even formed a chat group to communicate and hanged out to somewhere nearby the classes...but once we finished the courses finished, pfff .....nothing, even i even attempted to revive some outing ideas in our chat group but nothing.
And this wasn't the worse case, typically when a class finished (whether it is gym class or skill class...) everyone just rushes to leave home - there's no socialization in any form or shape after class.
As for social/activity clubs, people usually join with an already-established group of friends; they never seem to be interested to really know new people from the club itself, and make them part of their life outside the club at least.
Even if you succeed to obtain their facebook and add you or even their numbers, it leads to nowhere except more feed to your page - there's zero effort from over-25 or so people to form new friendships. I am not just talking about the opposite sex. No one really follows through.
The only thing that I've witnessed to work (to form new friendships or relationship) is mutual friendships, and not those activities/clubs many of you WPers keep talking about....but one should have an active social life to have that to begin with.
Who told you these things work? They actually don't, really.