if you feel good in 6 hour sleep, so its best for you... Its not sufficient for me, i feel some tired next day if i sleep 6 hour..
of course it is enough especially if you feel well. so it is ok, but if you feel that you are not so active and strong it means you are to sleep more.
Everyone is different but 8 hours is recommended. I certainly feel better if i have 8 hours rather than 7
People tend to need less sleep as they get older, and remember that everyone is different! Try 6, 7 and 8 for a week each and then see how you feel after each week.