Hello hima, 

I don't think that clothes till elbows are allowed. 

Wear Light Clothes ( Half T-Shirt or Shirt & trousers for boys and Half Sleeves Salwar & Kurti for girls), keep it simple and easy.Also don't wear anything with metal buttons as it caused problem to me last year. Avoid item which is prohibited by the AIIMS like pens, bottle, etc.

Also you can only take AIIMS 2019 Admit Card, photograph, and original ID proof.

Don't stress to much on the clothes. Be prepared and best of luck for the exam. 

Thank you.