Originally Posted by Lord Smexy:
“No, it's the sex appeal aspect that bothers me more, though I do think older men generally play the role better because they can capture that wisdom and feeling of paternity I often associate the character. I have enjoyed Peter Davison, Paul McGann and Matt Smith in the role however despite some of their flaws.”
Personally I feel Eccleston had gravitas, as did Tennant when required (he could turn from lighthearted to vengeful in a second) and even Smith (some great angry speeches) even though none were particularly old (especially Smith).
I'd agree that Capaldi's look does give him added gravitas and doctor authority, but I don't think an older actor is essential for that, just the right actor who can pull it off.