I Need Some Input From a Horse Person

Gentle Readers,

I need some input from horsy people.  What I need is someone to look at a very nice drawing of a unicorn/horse, and help me explain to the talented artist what is needed to clearly delineate whether this is a three month old colt or a full grown unicorn.  I've already explained that the colt would be as tall as the character (to its ears) and the adult would make the 5'9" character come up to the animal's shoulder.  (Unicorns are big suckers in my world, especially the males.)  Also, the colt would have a horn perhaps 6-9" long.  The adult would have a horn 2.5-3 feet long.

I can explain in one line what I think the problem is for me, but would like a second opinion/confirmation of this,  I pinged two horsy authors, but they are apparently very busy and haven't gotten back to me.  Does anyone else have a moment to look at a mockup?  (Insert of three month old Lipp included to help create explanation.)

Trying to keep my cover artist moving along...