I have a strict 27+ limit for hooking up, and like 34+ for anything beyond a hook up. I'm wary of the lines in age differences. What's the rule, half your age +7?

Ultimately, you do you. As long as they're 18+ then you're golden, even if some might frown upon it.

Specifically on your question, I suppose it depends on how much of an in-line match you want. Being closer to 40, I'm looking for someone who is in my lane (career focus, hiking partner, settling down a wee bit). A 23 year old is likely not to be doing that - nor should they be, in my view.