A simple question really - does regeneration inherently involve a "rejuvenation", ie. a transition to a younger or more able body?

The only reason I ask is this will be the first time in Doctor Who history that a younger doctor will regenerate into a visibly older doctor.

It'd make sense, but I don't think it does. The outcome is quite random.

Since Timelord bodies do not age or age very very slowly (the 11th Doctor looks 4 years older than in his first story but is in fact 300 years older) it makes little difference what the body looks like (in human terms) upon regeneration.




Saying that I believe the idea when Troughton took over from Hartnell was for a rejuvenation with Troughton meant to be a 200 year younger version of Hartnells body rather than a complete new body.

Actor-wise, Patrick Troughton was younger than Jon Pertwee.

Sylvester McCoy is only younger than Colin Baker by 2 months & 3 weeks

I'm not so sure. I've always thought Jon Pertwee looked considerably older than Patrick Troughton, even though there was only a year's difference between them.

Well Peter Davidson regenerated into a older Colin Barker

And someone has to regenerate into John Hurt, probably the oldest of the lot (assuming he hasn't changed much)!