6 months old baby not rolling
Every baby learns their milestones at different ages. My daughter started rolling at 3.5 months. Now at 6 months she does barrel rolls.
Your baby will probably be able to roll over when he's about six or seven months, when his neck and arm muscles are strong enough. Some babies manage rolling over as early as three months, and others take longer than seven. Your baby may be able to lift their head, push up on their arms, and arch their back to lift their chest off the ground. They may also rock on their stomach, kick their legs, and swim with their arms.
Some babies just skip rolling and go straight to crawling. If your still worried and concerned then you should contact your pediatrician.