Is it okay for 6 month old to sleep less?

I really feel you on this, the worry when you feel your baby isn't getting enough rest is so real. From what you've shared, he's getting a solid stretch at night which is great, and some babies do consolidate their sleep earlier than others. That said, since you're feeling unsure, it might be good to bring it up with your PD at the next visit just to be safe, especially if he seems cranky or hard to settle during the day. If he's generally happy, feeding well, and hitting his milestones, that's usually a reassuring sign, but your PD will be able to give you the best picture for his age.