English question, please help.?

The medical term is osteoporosis, a brittleness of bone due to calcium deficiency which causes distortion of the spinal column, and curvature of the spine, especially in old age, and more in post-menapausal women than in old men. A hunched back or crooked back is an extreme form and most people would deem its use insensitive or even unkind. You could say he was beginning to show a bit of a hunch, but it would be more PC to say he was showing signs of osteoporosis. Better still, just say that he is beginning to show signs of his age and is no longer quite so tall and upstanding as he used to be. If you need to be more specific say something about his upper part of his spine beginning to bend a little.

You can say they are decrepit.