hi,

see the eligibility criteria for jee advance is candidates must secure the cutoff percentile in jee main, as well as the marks criteria of 75% aggregate in 12th for general and obc candidates, 65% aggregate marks in 12th for sc/st category applicants. or the candidates must be in top 20 percentile in the respective education board. however for 2020 marks criteria is debarred , but in 2021 examination it may applied again. now there is also age criteria to fulfill,

Candidates should have been born on or after October 1, 1995. Five years relaxation is given to SC, ST and PwD candidates, i.e., these candidates should have been born on or after October 1, 1990. (applicable for 2020 admission).

A candidate may only appear in jee advance two consecutive year, that is starting from the 12th passing year and next year. so if you attempt 12th exam again in 2020, you may appear in jee advance in 2020 and 2021. but see you would have a gap of year of 4-5 years after 10th. which I would not suggest and it would be quite a issue for your placement. many students has obsession for iits to study and they waste their precious years. so it is not a wise decision to make. there is many private and govt institute in india which would give you a quality education to become successful in life. and you may go for masters courses in iits after completing bachelors.

so think before making any decision to another gap of year.

You may use Careers360 college predictor tool to know your predictable colleges

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer