Becoming a Den Chief is a great first step toward leadership.
Den Chiefs are Boy Scouts who assist a Cub Scout Den, taking direction from a Den Leader (adult) on how best to help the running of the Den.
Dens usually meet 1-2 times a month, so the time commitment is 1-3 hours per month, plus whatever other events the Scout wants to assist on (Pinewood Derby, Raingutter Regatta, etc. – not mandatory).
Den Chief is a Leadership Position within the Troop, so if a Scout is 1st Class or above and is not a Patrol Leader, Quartermaster, etc., that Scout really should become a Den Chief.* However, second year scouts are also eligible, and even first year scouts if the Scout is mature enough not to revert to Cub Scout behavior when they are with the Den.