hi,

see there is no age limit applied for appearing in jee main exam. but you may attempt jee main exam for three consecutive year starting from you 10+2 passing year. suppose you have passed 10+2 in 2018, then you may appear for the jee main in 2018, 2019 and 2020. for jee advance , ewhich is the entrance test for iits b.tech admission you can attempt for 2 times. if you pass 10+2 course in 2020, then you may apply for jee advance in 2020 and 2021. so there is no many times left, rather than thinking about year gap I would suggest you to give your best shot this year if you are applying for jee main exam, and lets see what happen, you may not know you may get a good score and got admission in top b.tech colleges.

hope you may understand.