this is an amazing piece!
I'm always so impressed about your technique! you're a great rolemodel for me!
anyways, i think the textures are just far beyond incredible!
It looks just like him! all ratios are perfect!
I also really like the way you drew his hair, with the combination of using dark hair and the high lights, with his beard it must have been a really precise job, and you did it very well!
Maybe it's an idea to make something that is really your own, by getting some portrait photos together and put them together in a way that it's expressive, photorealistic(that you already do), and has a little nonrealistic-twist to it, in the way that you draw something superduper realistic, but cant be a photograph or can't be actual reality, because of what's happening in the drawing. By example: add some effects.
Just amazing! cant say anything bad about it!