The wheelchair´s width is 58 and the door is 60 - I do it myself. Why (in the insurance company´s opinion) only children above 10 years can have it, I don´t get it?

The wheelchair´s width is 58 and the door is 60 - I do it myself. Why (in the insurance company´s opinion) only children above 10 years can have it, I don´t get it?