GE Predator:I believe that I can explain that. For 19 years, Luke and Obi-Wan lived on Tattooine, a desert planet with two suns. My theory is that those who are not native to Tattooine may experience some excessive aging over a period of years due to the two sun. And as we know from the prequels, Luke and Obi-Wan were not born on Tattooine.
Works for me. After all, look at Owen and Beru. Those harsh Tatooine desert winds and blazing sunshine "is doing murder to mesa skin".