How long do stomach flu germs live on plastic and wood like in a cosmetic closet, is 5-6 months enough to kill?

Yes. Norovirus, which causes outbreaks of stomach flu on cruise ships and in nursing homes, also affects many people in other settings. Studies have shown that on dry surfaces, without food residue, vomit residue, etc..., the viruses are dead after about 30 days (can be sooner) without disinfectant. Norovirus spreads easily because a very small number surviving virus particles can infect a person.
Should be! Most viruses last a few hours to days on surfaces. Examples: HIV a few hours; rhinovirus (common cold) 1 day; influenza 2 days, hepatitis (a&b) 1 week; norovirus 2 weeks; and small pox years. These are only guides, and the type of surface, light exposure, humidity and environment all make a difference.