Movies often perceive aging in dramatic fashion, but combined with the wonders of modern cosmetic surgery, hair color, and skin cream, we can take the vision versus reality and laugh:
This is stupid. When Michael J. Fox did BTTF 2, he was 28, laying an 18 year old. To compare their aging, you have to add the same number of years to Fox as they did to Marty…which means we have to see what Fox looks like at age 58. (And without makeup or any pre-public appearance stylist visits, etc.)
Lakawak has a good point. To show Marty McFly in the future 30 years, they had to age him 30 years. They couldn't just make him look 47, because he already looked like he was in his 20's.