Originally Posted by steven87gill:
“Always wondered if the Doctor ages like a human in each of his lives, if he did then surley he could regenerate naturally simply because of old age.”
I always believed that a timelord was almost immortal within the span of 13 regenerations and aged for the remainder of the lifespan of his/her current regeneration, regenerating when the body got old and warn out or some fatal trauma forced a regeneration.
Whenever we go to Gallifrey, we see young and old timelords alike. Mainly old and probably because of the pedestrian lifestyle not bringing about regeneration too often.
Finally, a timelord would grow old and die at the end of the lifespan of his 13th regeneration.
I never got the "trying for size" regeneration of Romana, but other regenerations have been seen; Borusa, the Master (who seems to defy the process with ease!), Castellan (I think but this could have just been another timelord!)