I used to clip an old hunter (25+ but young at heart) every year - wrinkly all over and oh, doesn't it take a long time!! And impossible to get a neat finish. He always looked like a clipped carpet
My Mac has lots of loose skin. He was quite overweight when I first got him and think that has contributed to it. When he had a vet check up a few weeks ago, vet commented that we could make another horse with his excess skin.
He is very good to clip, and I usually pull skin taut and OH clips.