The National Sleep Foundation last recommendations advise to regularly sleep between 7 and 9 hours per night for young adults. Nevertheless, those recommendations don’t take into account inter-individual variability and are strongly age dependant.
Sleep need varies a lot from an individual to another. As often, our genes explain most of these differences and we can not decide to be a short sleeper or a long sleeper. On top of that, sleep changes as we are getting older. Although it is not sure that the amount of sleep needed varies during adulthood, the way we sleep differs significatively. Older people hence often report experiencing poor sleep quality: it is shallower than before with regular awakenings during the night.
Yet, their sleep is usually more distributed and retirees tend to take more naps during the day. As you can see here, older adults have a more fragmented sleep and deep sleep ratio decreases.