In time dilation, does the "aging" referenced include biological/ physiological aging? for example, in the identical twin concept, is it possible for the twin who travels to space and back to have actually aged so much that by the time he returns his brother is dead of old age? in other words, does time dilation affect physiological processes?
Time dilation affects time itself, which means that it affects absolutely everything. For the twin that traveled away and came back, literally less time will have passed for him than for the twin back on Earth. So he will have aged less, his shoes will have worn out less, the turbines on his spaceship's pumps will have rotated fewer times - everything.
Every object has its own frame of reference. So, time dilation only means that, for this case, the twin in space is aging slower according to the twin that is still on Earth. However, according to the twin in space, he is aging normally in his frame of reference. In other words, yes, time dilation does affect biological aging. It just affects it differently depends on whose perspective you're with.
Time dilation on living creatures (and more in general to any experiment scenario not limited to light or e.m. wave propagation phenomena) is at the moment still only a speculation of the applicability of SR theory and no experiment has been conducted as far as I know to prove it. To note that such a situation, i.e. with different ageing scenarios depending on the reference frame you choose is contrary to a single physical universe assumption, and would led to the generation to infinite ones just based on the definition of an arbitrary inertial reference frame from which to look at the experiment.