My DS could lift our vacuum cleaner off the floor at 6m whilst in my arms. It's a DYSON! I struggle to lift it up the stairs (when we had stairs)!

So I say it's normal.

Then again, DS has had a crowd of little girls (pre-school age) all cooing over how strong he is when he lifts and carries quite normal things. Maybe he is stronger than I give him credit for? It is scary what he can lift and carry around these days.

He was holding his head from birth, btw. Which I thought was perfectly normal.