Who is susceptible to impetigo?

Everyone. Impetigo is a skin infection. Anyone can have this occur.
Contagious to anyone. Impetigo that is on several parts of the body is very likely contagious enough to spread to other people. People with cracked or otherwise irritated skin will have more microscopic breaks in the skin surface, so they are more easily infected by impetigo bacteria.
Anyone. Impetigo (skin infection with strep/staph) can occur at any time the skin is broken (dry and cracked, cuts, scrapes). We all have bacteria on our skin or we get it on our skin throughout the day. Usually intact skin is a great barrier to infection, but once broken the bacteria can get in there and "start a family (infection)." keeping skin conditioned, good overall hygiene and bathing can help.