Two occasions, both in London, both decades ago and both women in their 50s.
First affair was in late 1986; I was 30, she was a slim, upmarket bottle blonde with a flat in St. John's Wood, a posh area. We met at a party and I chatted inconsequentially to her and her sixysomething apparently would-be paramour, and the two of them gave me a life home- she slipped me her number in the car telling me quietly to phone in half an hour. I did and she invited me over then and there. She was an enthusiastic partner but unfortunately not ticklish in the least though I tried a few times, over the next few months, even on one occasion when she allowed me to tie her to the bed first. She was most insistent that she was taking care of contraception on her own, so I left that up to her. She was a somewhat maudlin/ratty drunk; it ended when I went over one night to find her sniffling over a near-empty bottle of expensive wine, and she held me before bursting into quietly refined British hysterics and sobbing, 'I've lost our baby!'
I comforted her, while happening to look over her shoulder at the mantlepiece mirror, which revealed me looking wildly delighted at this turn of events. I had no idea I'd been drafted to provide her with a child.
The next, in the early 2000s when I was newly-divorced and in my mid-40s was a long-haired and attractive Anglo-Portuguese woman who spoke perfect, unaccented English. In her mid 50s and encountered at a picnic, she rode pillion and held me rather tightly when we motorcycled back to her basement apartment. One thing led to another and she allowed me to tie her to her futon frame. I was quite gentle with her, but as she seemed to be really enjoying herself I had her in happy hysterics pretty quickly. Her feet were especially responsive, and at that point she began begging very prettily indeed in Portuguese so after a while I untied her and we finished things off in a conventional manner. We carried on in the same vein for a month or so, including the tickling but whenever she'd introduce me to her similarly-aged friends on social occasions I felt like I was being presented as a young, prizewinning bull at an agricultural show, and it made me a bit uncomfortable.
I'm now married to a younger woman and much happier tickling her.