Hi Ramit, thanks for your query.

It is good that you are thinking of admitting yourself in some coaching institute for preparing yourself. But you see that there is limit that till how many year you can sit for the exam after 12th.

For appearing in the JEE (Main)-2019 examination there is no age limit for the candidates. The candidates who have passed XII examination in 2017, 2018 or appearing in 2019 irrespective of their age can appear in JEE (Main)- examination 2019. The candidates should satisfy themselves about the eligibility of age limit requirements of the Institutes in which he/she is desirous of taking admission.

Hope you understand that if you attempt the exam after two years, it would be your last chance to attempt. 

Hello,
The student is supposed to pass 12th with an aggreagate of a minimum 75%. Whether or not you are taking coaching is none of anybody's concern. If you need good rank and want to get an admission in iits, nits, iiits, and renowned institutes throughout the nation, it is better to take coaching from a renowned coaching centre.
If this is not what you are looking for, kindly mention your question in detail, to get a defiinite answer.
Good Luck!