@bluebullets If it helps, the quality of the ink today is better than 20 years ago (so I hear). So todays ink should last better, and safer as we use synthetic azo dyes instead of metals to make color.
Of course you need to take care of your ink as well.
You said you already have tattoos, but is more concerned about ageing for sleeves. From what I have seen, I think sleeves age really nicely!!
Sorry....I dont have a 20 year tattoo but i just wanted to say I went for a sleeve over individual tattoos for the exact reason you are not😂
(But Im open to one piece shots on my leg or other arm, just need my wallet to recover)