Swings and roundabouts really.
Younger people have more options available in terms of more people their age that are single, but there is also more 'competition' around.
As you get older, being single can feel a bit tough sometimes in that you tend to find most people your age are in steady relationships or have families, but there are always people coming out of relationships, getting divorced, or to be honest having affairs. There's also a different dynamic between single people that kicks in when you get to late 20s or older, in that single people are more available in terms of time than those especially who have families, and also more up for doing stuff with other single people, so when you do find singles that you are interested in there's more of a chance of hanging out together and giving it a go than when you're 20, and the person you are interested in is probably going out 4 times a week, on Tinder with multiple dates already arranged, and basically you're just one of many on their shortlist.
Also it depends where you live, in cities it's easier to meet other older singles. London especially, given the lack of affordable housing, is a place where single people are driven together through houseshares, so whilst the concept of living like a student in a shared flat in your 30s/40s might sound unappealing, it does mean if you are single you're likely to find it easy to find others in the same boat and not feel like the odd single loner in your social group.