lookin'good sofar...
I think the lips and the area around the mouth needs to be done a little more...

if this is the mouth --> =
than you see the two rinkels sided the mouth --> (=)
loose those...try to make it more even..
and the thing what might work that it will look more like him is the eyebrows.... try to make them and fit it to the reference image...
With the minor tweeks around the mouth and eyes...I guess it will start to end up nicely!!
goodluck! let us see your progress