When does phimosis go away?

Phimosis is a natural condition in boys from birth until between anywhere from 5 and adulthood. The skin is fused to the glans and normally detaches gradually during this time in 95% of males. The other 5% need treatment of some sort. From manual gentle stretching, with or without topical steroid cream to surgical procedures.
Preputioplasty is a minor surgical procedure that is used to make the opening wider. A small incision is made in the tight band of skin in the form of a slit.
Circumcision is a surgical procedure to remove the complete foreskin and is a more severe and radical treatment.
It is different for every man. From birth to 18 years there is a gradual decrease in incidence. No studies have been conducted past that age. If you want to speed up the process you can get a prescription of steroid cream from a doctor.