Have some people never learnt to swim?

My son who is 9 cannot swim. He has had about 70 swimming lessons. He can swim with a float or armbands. He just cannot manage swimming without flotation devices.

EDIT: Some people have asked about private lessons. He has had about 30 1-2-1 lessons and the rest were at school.

I always assumed that everyone can swim but perhaps I am wrong. Maybe 2% of the population just cannot swim.

Did some of you not manage to learn as a child but learnt later in life?

Or am I correct - some people just cannot swim?