Yes! He will be eligibile to appear for the MHTCET exam. You can also check here the MHTCET Eligibility Criteria for NRIs. But in this case your son will not be eligible to take 15% reservation in any government engineering colleges in India. There is special NRI quota is available in top prestigious colleges in India, 15% seats are reserved for NRIs under DASA / CIWG quota. 

In my opinion if you wish to take admission under DASA / CIWG quota. Students must have completed his 11th and 12th from the foreign school abroad.

We also compiled an eBook For NRIs students. You can download from here: Download Now DASA / CIWG eBook.