My aunt is in her 80s, never married and no children.
I think she has moments of regret, and gets lonely. She does get upset about it from time to time - however that’s most likely because it wasn’t so much an active choice on her part to never have children, more a case of she had other things going on and sort of imagined it would possibly happen one day except it didn’t.
She has, on the other hand, had the most fabulous life. A really interesting career, lives abroad and has travelled the world many times over, some wonderful adventures, great stories, so many hobbies and interests, a really tight knit circle of wonderful best friends, and other friends all over the world. Even now at 86 she’s out and about every day and most evenings (was working until the first lockdown), swimming in the sea, walking, volunteering, drama society, choir etc etc. currently doing a music course at the local university. Forever out at dinners and dances and concerts. And she’s always been very close to me and is now a bit like a grandparent to my daughter.
She says herself that whilst she feels the lack of a child of her own, she wouldn’t have had the life she’s had if she was a mother, and on balance she’s not sure she’d swap.