Hi

For JEE mains you need to have maths as a subject in 12 th standard. Without maths you are not eligible for JEE mains. There is no age limit for JEE mains and one can sit for the exam for 3 consecutive years from the year of their passing 12th. For example if some one pass their 12 th in 2021 he is eligible for JEE mains 2021, 2022,2023. JEE mains is held 4 times a year and therefore you get a total of 12 attempts. A person appearing for 12th standard exam can also give JEE mains. So if you repeat your 12th standard with maths you are eligible for JEE mains from the year of your passing the 12th standard.

As for admission in government colleges that will depend on how much you score in JEE mains. With good score above 95+ percentile you can get NIT'S and IIITs

For more information look up the eligibility criteria and other requirements:

https://www.google.com/amp/s/engineering.careers360.com/articles/jee-main-eligibility-criteria/amp

hope this helps