But I am giving neet in 2020 exam at that time I will be 18 yrs old

Yes, then it is fine. You have to be 17 years or older in the year in which you are sitting for the exam.

Is there any option like I don't prefer counseling and attempt the exam??

I have passed 11th while preparing for neet,it was avarage. But due to my age I have 3 more years before examination now. So should I repeat my 11th then 12th and then target.bevause my seniors said that 11th is more important for exam. Or should I continue to 12th.
In short my question is that I have passed 11th class coaching with avarage performance.and I have 3 more years to prepare before exam.what should be my approach 11th repeat or continue to 12th. And what after that.