Dear Rahul, if you will pass your 10+2 in 2020, your attempts will be counted from 2020 if you haven't attempted JEE before. There is no upper age limit for JEE either. You can attempt JEE Mains consecutively for 3 years. The exam will be conducted twice a year and the attempts for 1 accademic year will be counted as 1 attempt. This is about JEE Mains. It is important to know about JEE Mains before knowing about JEE Advanced because only those Candidates who qualify in JEE Mains can appear for JEE Advanced. And you can appear for JEE Advanced for 2 consecutive years. So lets say if you appear for JEE Mains and qualify in 2020, you are eligible for appearing for JEE Advanced in 2020 and 2021.