What is the ruling on the prayer of a young man who wore an ornate chiffon women's skirt to cover his 'awrah during prayer, while he possesses shorts that do not cover the knee, claiming that it is not imitation but rather for covering the 'awrah?

It is not permissible for a man to imitate women in dress, and this is one of the major sins due to the curses mentioned concerning it. There is no difference whether these clothes are worn in public or in private. If a worshipper covers his 'awrah with women's clothing, there is a difference of opinion among scholars regarding the validity of his prayer. The prayer is valid according to the majority of scholars, but he must repent to Allah Almighty and beware of His punishment, and not revert to wearing any women's clothing, neither in prayer nor otherwise.