I don't know, tatoos are not my thing. With Heath they seem sort of symbolic of places he has been or people/situations that are important to him. With my own son, I personally think it was a fad dare. LOL
And I know several older navy guys with tatoos that looked really good when they were young and tight, but when the skin starts to sag, wrinkle, and loosen, they are almost unrecognizable if they don't tell you what they were. Heard one woman say that when her son wanted a bird, she told him 35 years from now it will look like some kind of monster out of a nightmare. Had to laugh, but it could well turn out to be true.
A lot of how it ages will depend on size/detailing and where they are placed and the type of musculature under the skin.
There is a rumor/blog going around that Heath's Joker will have gray skin and lots of facial scarring--and he won't be wearing a purple suit either, more like raggedy jacket pants that he has put on without much thought--wonder how much input Heath had into that?? LOL They also say that there won't much funny about him, more scary, in keeping with the scary scarecrow type sinister feelings in the first one.