I can offer two constructive points that leapt out to me, in case they're of any help to you at this early stage:

First one is to echo Teyon's point about the trapezius and neck... that stood out to me as not quite right.

He has the appearance to me that he's craning his neck and tensing up his trapezius... which, assuming that's a more neutral, zero-type pose he's meant to be in at this point, I guess wouldn't be desirable.

I think it might be the length of the neck as much as the trapezius muscles that seems a bit out to me here...

...all this may be accentuated by the viewing angle... seeing him straight on might help?

Second is that the hands look a tiny bit large relative to the head to me.

I'm pretty sure either the head looks a bit too small or the hands a bit big... or both could be out by an even smaller amount each way... we're probably talking fairly small amounts proportionally.

It's entirely possible that you are working to a real life reference model who has these exact proportions though!?

My judgements will be founded on my personal, "built-in" conception of average norms and certainly aren't scientific...

Were these two of the areas you mentioned being bugged by still?

Are you aiming to create a Mr Average character that can be morphed in any and all directions or are you going for a particular look out of the box in terms of physique?

Anyway... looking forward to seeing Lucas develop - many thanks ;-)