Melatonin from what i understand is a hormone produced in the body that gradually decreases w/ age. So considering that, maybe it would work better for older people. I also found read that it's a very potent antioxidant, even more than C,E, and A.
About Benzodiazapines, not all of them have sleep inducing properties. Dalmane and Halcion have hypnotic, sleep inducing effect. Others like Ativan and Xanax reduce anxiety and don't make you sleepy. From what i remember, they have their own receptors in the brain and they potentiate GABA (gamma-aminobutyric acid) which is an inhibitory neurotransmitter.