I've seen what Mark looks like now with the wrinkles and I'm don't entirely think it's right. Without the bags under the eyes I think it looks much better. So maybe the rule could be 35-40 Side wrinkles, 40+ Side and Bottom wrinkles. Only my opinion :P
It's true that the wrinkles are not so accurate for some drivers but what is true is that there were drivers that look older than others but this is a way to show that they were here so much time. What you say about +40 for wrinkles at side and bottom maybe we couldn't see it in F1 after Schumi hehehe