I was never crazy about the stock photo rule. On the covers the characters don't really ever age.
Depends how much effort goes into the postwork. The cover of
Serpents Amongst the Ruins, for instance, used a stock photo of Harriman but it was enhanced to make him look older. Also, some of these actors have likeness approvals and might not like anything that makes them look aged.
Painting is generally better to make characters age, but then you run into the problem that one artist's rendition might not look like the next, as was the case during the NJO (one cover had an older Luke looking like a grayed, slightly lined version of himself from ANH, another had him looking more like modern-day Mark Hamil, and the difference is quite sizeable.)
