Yes. There are many pre-trained model. You can then use transfer learning to build on a pre-trained model to benefit from the existing computational effort.
I frankly don't see why it couldn't add more years to 50y. Moreover, it could likely "unage" over 50y to 20y, just by inverse of their aging method. GANs are unbelievably powerful.
For a start, yes. A proof of pricinple would be nice. Would probably look very shitty, but would use very little bandwidth.
I read about a fictional system like this in "A fire upon the deep" by Vernor Vinge a long time ago but never thought it would be feasible. There a scene of an entire room of people interacting was being deconstructed/reconstructed for a video chat using low bandwidth.
The article doesn't point this out, but in GANs, the parameters actually move on a continuous range. In other words, they don't just have several of your pictures, they've got all sorts of movies :
A movie where your face starts out "neutral" and becomes angry. A movie where you start out angry, go to surprised and end happy. And so on.
Here it is: one glorious hour of walk through the latent space of faces. You can "feel" the geometry of the latent space and its meanderings. https://www.youtube.com/watch?v=36lE9tV9vm0
Generated with Progressive GAN in high resolution. The quality is mind blowing, highest ever attained in any GAN. Author: NVIDIA
Well, no, you can't create information that doesn't exist. They don't have any better source to match against your blonde-hair picture than their imagination. The novelty here is that they may outsource that imagination to the machine now.