Sure -- you could see Smith's youth ITSELF as a sign of the Doctor in denial and Capaldi as a sign of the Doctor embracing his age.
Notably, Capaldi, at 55, is the same age Hartnell was when the show began. Though I gotta say, Hartnell LOOKED a whole lot older than Capaldi does. (Richard Hurndall played the First Doctor at the age of 72, and bore a pretty striking resemblance to Hartnell at 55.)
In fact, what the hell -- here's a rundown of the age each actor was during his run. (I'm going by airdates; I realize that doesn't necessarily reflect the actual age the actor was when the episode was filmed, but it should be within a year, anyway, and that's close enough that I'm not going to go to the effort of looking up actual shooting dates. Also, source is Wikipedia, so of course any of this information could actually be bullshit.)
Hartnell: Born January 1908; played the Doctor November 1963-October 1966 -> aged 55-58 (and appeared in The Three Doctors in December 1972/January 1973, aged 64)
Troughton: Born March 1920; played the Doctor October 1966-June 1969 -> aged 46-49 (52 in The Three Doctors, 63 in The Five Doctors in November '83, 64 in The Two Doctors in February '85)
Pertwee: Born July 1919; played the Doctor January 1970-June 1974 -> aged 50-54 (64 in The Five Doctors)
Tom Baker: Born January 1934; played the Doctor June 1974-March 1981 -> aged 40-47
Davison: Born April 1951; played the Doctor March 1981-March 1984 -> aged 29-32 (56 in Time Crash in November 2007)
Colin Baker: Born June 1943; played the Doctor March 1984-December 1986 -> aged 40-43
McCoy: Born August 1943; played the Doctor September 1987-December 1989 on series, May 1996 TV movie -> aged 44-46, 52
McGann: Born November 1959; played the Doctor in the movie -> aged 36. To date we've never seen his regeneration; if the rumors are true and he's going to show up this year, he'll be 54.
Eccleston: Born February 1964; played the Doctor March-June 2005 -> aged 41.
Tennant: Born April 1971; played the Doctor June 2005-January 2010 -> aged 34-38; returning in November at age 42.
Smith: October 1982, represent! Played the Doctor January 2010; concluding in December 2013 -> aged 27-31.
Capaldi: Born April 1958; begins playing the Doctor in December 2013, aged 55.
And, for the hell of it:
Richard Hurndall: Born November 1910; was 72 in The Five Doctors
Richard E Grant: Born May 1957; appeared in Scream of the Shalka in November-December 2003 -> aged 46
John Hurt: Born January 1940; age 73
SO:
Oldest by start date: (Hurt, Hurndall,) Hartnell/Capaldi, Pertwee, Troughton(/Grant), McCoy, Eccleston, the Bakers, McGann, Tennant, Davison, Smith.
Oldest by end date: (Hurt, Hurndall, Capaldi?,) Hartnell, (Capaldi?,) Pertwee(/McGann if he shows up in November and we count that), McCoy if reckoning by the movie, Troughton, Tom Baker, McCoy if reckoning by the last episode of the show(/Grant), Colin Baker, Eccleston, Tennant, McGann if only counting the TV movie, Davison, Smith.
So mostly the same list except, as you'd expect, Tom Baker's extra-long run, Eccleston's extra-short one, and the ambiguity of how to count the movie.