I think it could be somewhat of an optical illusion created by a couple of things:
1) Weight loss, look at the point of his hip suggesting loss of muscle mass
2) His front feet being slightly lower than his rear.
These two things could give him the look of a sway back, and possibly contribute to the appearance of a pot belly. However, if he is underweight, he may be eating some less desirable plants that could be filling his paunch up fuller than normal.
All in all, I still think it is a younger deer. Good photo. Gets you thinking!
txhunter58
venor, ergo sum (I hunt, therefore I am)