I am interested to read about posters whose hair has got wavier as they have got older. Mine remains, in my 70s, as dead straight as ever.
The only time my hair has curled (except for when my mother tried unsuccessfully to coax it into ringlets as a child) was when I got very severe eczema in my hair. The hair on the top of my head where the the eczema was particularly bad became exceedingly curly (I have short hair). I thought I looked rather like those pictures of Queen Alexandra, with tight curls on top and smooth and close to the head round the sides. DH said I looked like a coconut, as the affected hair had faded on colour, short red rough red hair on top, surrounded by straight smooth dark hair.
Thankfully when the eczema cleared, my hair grew back straight and dark.