This depends on how the cigar is stored or kept. If the cigar is kept in a properly maintained humidor at 70 degrees and 70% humidity, it will stay fresh for 100 years or more.
If a cigar is not stored in a humidor or any storage device with controlled temperature and humidity, then it will start drying out in 30 days. So smoke it before it is 30 days old.
The cellophane wrapper that cigars are shipped in will not preserve any humidity because they are permeable (tiny holes or pores) which means air can move through the cellophane. The cigar will still dry out in the cello wrapper.