When I was 18 or 19 before I started dating my future wife I hooked up with to other women I worked with at the grocery store.
The first was a 23 year old single mom. She was cute and fun but had some baggage, namely an on again off again relationship with the guy she had the kid with. We went out maybe 8 times, ending up in bed on the third. The thing I remember the most about the first time was when I was unsnapping her jeans to reach into her panties she stopped me saying "no, don't. If you do that I won't be able to stop." I remember thinking well duh, who wants to stop. Of course a few minutes more of making out and she didn't stop me the next time I reached down. She finally decided she was going to try and make it work with the baby daddy, ending our fun together.
The second women was a 28 year old brunette, who was still in college working on a masters. I also found her very attractive. She came off kind of snobby because she was so quiet but I was assigned to be her grocery bagger quite often so I got to know her as a friend. Fast forward to a company Christmas party. They held one of those date auctions to raise money for something. This lady was up on the auction block and I won the bidding. On our official date nothing happened other than dinner and a movie and a lot of talking. I found out she was kind of seeing somebody but she didn't know how serious the guy was yet, another on again off again type of relationship. Not that I was any kind of ladies man or anything but I sensed an opportunity, laying on the compliments about how beautiful she was and the guys an idiot if he can't see that etc. I got the typical "your sweet, only if you were older" etc.
About a week later I talked her into going out again. After dinner we went to a bar (not a trendy enough place to need someone carding people at the door) that had a DJ that night. After some more talking and drinks (her not me) we hit the dance floor first for some fast ones then a slow set started and we stayed out there. I pulled her close against me as we swayed to the music. Holding a good looking woman close had the expected result of giving me an instant boner, but I did not try to hide it. By the second song she was pressing up tight to me and resting her head on my shoulder. When the fast songs came back on I asked if she was ready to leave. She was. As I drove her back to her place I still wasn't expecting anything but she asked me to come in. Soon we were naked in her bed. It's funny, now that I am 45, 28 seems so young but at the time I found her "mature" body intoxicating. She just had the most gorgeous curves, and full breasts. I loved watching them hang and sway as she was on top riding me. When we finished and were lying there she kept bringing up the age difference wishing I were older. We had that same conversation two more evenings before she really meant it, deciding she couldn't see me out side of work any more. She then finished her masters and left the grocery store about a month after that. I also found out she was now engaged to the on and off again guy.
So that was the only time I have been somebody's "boy toy". After the 28 year old it was back to girls my own age. I do like to joke with my wife though about being an older women. Because of where our birthdays fall, for a short time she is "2" years older than me. So to answer the question of "how old would you go?" I will just say as old as my wife gets and as long as she puts up with me.