Life span of new bags and shoes kept in storage?

I'm not sure there is actually one. I'm don't know why your items are deteriorating. My grandmother died last year and when we were cleaning out her house there were closets full of ladies dress shoes in regular cardboard shoe boxes that had not deteriorated at all from ~ 1950 - 1990. Not sure about the humidity but she kept the temperature in her house around 21�C year round.