As for looking older than the body you've regenerated into, Capaldi is himself younger than he looks.
So were Hartnell and Pertwee. (Terrance Dicks's novelizations often referred to the Third Doctor's "young-old face.") Although unlike the others, Hartnell was unusually decrepit for his age, due to his heavy drinking and smoking. Which was bad for him, but good for the franchise, because if he hadn't had to step down, we never would've had regeneration, and the show would've probably ended by 1970 or so. (Although seeing "The War Machines" recently made me wish we could've seen the First Doctor working with UNIT. That was the only time we ever saw him in the role of an advisor to present-day Earth authorities, but it's a role he took to extremely well. Hartnell was in fine form in that serial.)