I'm almost out of my 40s and I definitely support you in doing whatever you like and not overthinking the midlife crisis thing.
That said, if I had the inkling (pun intended) to get a tattoo I would actually wait until this lymphoma association is verified, because if if it turns to be real, and then I get a lymphoma, I would feel very stupid. But then again, people smoke and do a lot of things that are objectively bad for their health. In short, I would not do it myself, but I would not judge you at all if you did.
If there is a link, I'd guess you're probably a lot safer getting tattooed at 50 than at 20 given you've (statistically) got much less time for any adverse effects to start showing up...
I don't know if I'd conclude it. What about the possibility of that the tattoo association is only at higher ages, because of some effect where younger people have a better immune system to ward off any immediate dangers of the tattoo ink and then it becomes inert. But getting it at 50, your body is less able to dispel the problematic compounds in the ink. Basically saying the ink's problems could just be front-loaded the first couple years. Without understanding those details (risk associated with when the tattoo was received and short-term vs. long term risk), I'd be wary about deciding 50 is safer than 20.
That said, if I had the inkling (pun intended) to get a tattoo I would actually wait until this lymphoma association is verified, because if if it turns to be real, and then I get a lymphoma, I would feel very stupid. But then again, people smoke and do a lot of things that are objectively bad for their health. In short, I would not do it myself, but I would not judge you at all if you did.