Because you aren't doing anything to change it, slow down when you talk and practice talking in a deeper voice. I'm guessing when your voice started to crack you chose to concentrate on keeping high rather than lowering it and now it's become a habit.

Puberty usually. Check your parents voices, ask them. Voices are genetic.

Tension.

Relax and try let it drop. A voice coach would give you throat relaxation lessons.

relax and take it easy

at 50 you might look like a 30 year old

that will be great !!