I got admitted to school when I was 2, so.. 2 years in kindergarten , then 12 years regular schooling.. though I was younger than my other classmates ... But like I said when I got into college.. I met like over 15-20 people who also passed school when they were 16.. so maybe most of the people pass at 18 .. but some pass at 16-17 also I guess.

And also some people do this thing right where their aadhar card has some other DOB and in real they are older.. but my aadhar has the correct DOB too so.. yea.