Strictly speaking, every science fiction tale presents its own version of future and therefore there are as many science fiction universes as there are science fiction stories. Many SF tales follow dictates of a particular subgenre like Cyberpunk or Space Opera of which, see the separate entry.
... age of 18, 8.1% from 18 to 24, 29.9% from 25 to 44, 23.8% from 45 to 64, and 7.9% who are 65 years of age or older. The median age is 35 years. For every 100 females ...