Yes your hair can indeed change texture every 7 years because after 7 years your hair has continued to grow and pushed out old hair.
So as your older hair pushes out then newer hair grows out of your head so when that happens you basically get new hair every 7 years or actually everyday new hair is being grown.
Also as the older you get the more your hair usually changes due to hormone changes especially when you're a toddler, child, teen and then adult.
Over the course of those years your hair texture and even color of your hair can change.
When my son was born his hair was black and now he has blond hair and it used to be curly when he was a toddler and now that he's almost 10 years old he has straight blond hair now.
The hair on him will likely change some more into an even darker color again the older he gets.