My baby was sleeping on his tummy since birth so he tend to have a stronger neck earlier. He could lift his head from tummy position at about 6-8 weeks.
My friends whose baby slept on his back from birth can lift his head from tummy position at about 3 mths.
When you put your baby on his tummy, does he know how to lift his head? How much tummy time do you give your boy during play?
Even though my baby could lift his head from tummy position, the neck muscles are still weak. Meaning that when I try to sit him up, I still need to support his head.