hii

yeah you son is definately eligible for JEE advanced but make sure that you son full fills the below criteria

Criterion 1 – Performance in JEE Main 2018

Criterion 2 – Age Limit

Criterion 3 – Number of Attempts

Criterion 4 – Appearance in 10+2 (or equivalent) Examination

Criterion 5 – Earlier Admission at IITs

Performance in JEE Main 2018 – The candidates will have to qualify JEE Main 2018 examination and be among the top 2,24,000 (including all categories) candidates. The percentages of various categories are: OBC-NCL (27%), SC (15%), ST (7.5%) and Open Category (50.5%). Within each of these categories, 5% horizontal reservation is available for PwD candidates.  

For the greater information kindly refer

Https://engineering.careers360.com/articles/jee-advanced-eligibility-criteria 

hope this helps