Noses keep growing as people age. If someone's nose grows slower, they look younger for longer. It's a key diferrence, as much or more that hairline or wrinkles.
I suspect it's directly proportional to the amount of drugs each has consumed, honestly. That, and sometimes putting on a few pounds can make you look a bit younger, but sometimes it just makes you look so fucking bad.
Regarding Tom Cruise -- I can't see it in that picture, but there are certain angles where you can really tell how much work he's had done. And we're entering uncomfortably un-grey hair territory, I think.