Peter Davison's Doctor had the first Doctor's temper, he could snap at anybody and he was always very kind about it. But I never got the impression that Smith's Doctor was an old man even when he was in an old man's makeup.
Young and old are relative Tom Baker was 39 wen started playing the Doctor and both McGann and Tennant were in their 30s. Hartnell, Pertwee and Capaldi were in their 50s and really Pertwee and Capaldi's Dcotors act much younger than the actor's ages. The only real limiting factor in an older body is the health of the body, not the age of the body of the Doctor. The fourth Doctor did seem worn out by the end of Baker's era and IMO he looked it.
Young and old are relative Tom Baker was 39 wen started playing the Doctor and both McGann and Tennant were in their 30s. Hartnell, Pertwee and Capaldi were in their 50s and really Pertwee and Capaldi's Dcotors act much younger than the actor's ages. The only real limiting factor in an older body is the health of the body, not the age of the body of the Doctor. The fourth Doctor did seem worn out by the end of Baker's era and IMO he looked it.