You didn't mentioned the session in which your son scored 205 marks. Without this information we can't predict the expected percentile or score for JEE MAINS 2021.

But you can follow the link below for the JEE MAINS rank predictor 2021, you can put the appropriate information there and you will get the expected JEE MAINS Rank and percentile for free.

For rank predictor visit the link below:

For JEE MAINS college predictor you may visit the link below:

I hope this answer helps. All the very best for your future endeavors!