Anecdote warning:

My experience living in a city with a non-trivial homeless population is most homeless -- at least the visible ones -- are predominantly able-body young men (and increasing women too) in their 20-30s. We're not talking factory workers who got laid off after 15 years due to outsourcing. They strike me more like urban, drug addled version of Chris McCandless from 'into the wild'.

Of course this experience may not reflect other regions.