I've attempted to answer this puzzlement myself and PEW research says:
"Some age groups have a higher share of singles than others. Adults under 30 are the most likely age group to be single, with roughly half (47%) falling into this category. In contrast, 30- to 49-year-olds are the least likely to be single (21%). About three-in-ten adults ages 50 to 64 or 65 and older say they are single."
I suppose my personal bias is that while being single is a valid lifestyle that is a lot of singles at age 50 to 64.
I don't find the 30 to 49 range of 21% to be that big (at least a percent or two are likely single for expected reasons like entering a priesthood or being asexual) and while the below 30 single rate is a little surprising the difference between an 18 year old adult and 28 year old adult is too big to draw conclusions.