How young is too young to have a smartphone? A Colorado man thinks that age 13 should be the limit and is leading a campaign to ban the sale of the devices to children under that age. Retailers who violate the ban could be fined $500 after first receiving a warning. The ballott measure he's proposing would establish the nation's first legal limit on the sale of smart devices. The man needs about 300,000 voter signatures for the proposal to make it on Colorado's 2018 ballot.