how old is too young for tummy time ?

I started on day one. at 1st is was just on my chest then on the floor few minutes at a time a few times a day.

My cousin had her baby do tummy time starting after birth..baby on chest ay first then on the boppy and then without the boppy...

oh ok i just wanted to check because my baby girl is holding her head up by herself already & i want to start her with tummie time