For JEE avanced you need to have folowing eleigibilty criteria to be met to sit for the exam:-

• the candidate has to qualify JEE main and has to be amongst top 2.24lakh students.
• the age limit prescribed is that candidate should be born before Oct 1st, 1994
• should have cleared all five subjects from class 12th and should have attained minimum 75 percent aggregate marks.
• The candidate is allowed to take two attempts in consecutive years that is 2018 & 2019.

Ypu can now attempt for next two years by starting from now since, you will be giving reattempt to class 12th.

Below some great preparation tips have been shared for reference:-

https://engineering.careers360.com/articles/jee-advanced-preparation-tips-physics-chemistry-and-mathematics

All the best..!!