I have an older mare that toes out on all 4 feet. She is trimmed to her own conformation and she gaits very well. She is a Fox Trotter.
Many of these horses could have possiably been corrected had they had the proper trimming as youngsters, less than a year old. I believe once the joints close, at a year or so old, a professional farrier would be the one to tell you what the possiabilities are. Trimming and shoeing for balance and conformation are very important no matter how much we would like to straighten their feet.