The flexibility and range of motion of the calves normally limit dorsiflextion of the foot.
I read in Stretching Scientifically
(2003), T. Kurz, that one sign of a tight Soleus is difficulty in squatting. I believe that tight Soleus is a problem of mine. I have balance problems squatting (plus other ROM issues from an old knee injury).
To determine whether the range of motion of a joint is within some norm the ROM has to be measured or otherwise estimated (wall test, etc.). Here are some sites that bear on issues of measuring/estimating ROM for dorsiflexion, squatting, stretching, and some discussion of possible genetic dorsiflexion limitation, etc..
If injured, forcing stretches or measuring/estimating range of motion may risk farther injury.
I just started reading these links and have not evaluated them very much.....
Calf - ROM & Stretching (See the wall measurements for estimating ROM.)
Does stretching increase ankle dorsiflexion ... [Br J Sports Med. 2006] - PubMed (You can view the full text by clicking on the "Free.." icon upper right.)
Squat Technique & Ankle Dorsiflexion
Frozen Ankle, Ankle Mobility, and Squatting | Eric Cressey
Calf Exercises & Stretches
High Performance Training, Personal Training Wall Bent Knee Calf Stretch
Re: Reasons for Limited Dorsiflexion (Is the ankle just too stiff or somehow bone limited and tight calf muscles are not the limitation?)