Hi

There's no age limit for EWS certificate. So, you don't need to be 18 years old, you need EWS certificate on your name for jee main and for ews reservation anywhere.

To help you further,

Ews eligibility which is provided below:-

-) you shouldn't be covered under the scheme of reservation for OBCs ,SCs and STs

-)your gross family annual income from all sources i.e. salary, agriculture, business, profession, etc. must be less than 8 lakh rupees

-) irrespective of the annual family income one won't be eligible for ews reservation if his /her family owns

a) agricultural land of 5 acres and above

b) Residential area of 1000 sq ft. and above

c) Residential plot of 100 sq. yards and above in notified municipalities

d) Residential, plot of 200 sq. yards or  above 200 sq. yards in  the areas which are those other than the notified municipalities.

You can check the same at its official page the link is provided below

https://dopt.gov.in/sites/default/files/ewsf28fT.PDF

Even if you don't have your ews certificate right now ,you can download the self declaration and fill it and submit it in place of ews certificate. The self declaration/ undertaking form for category you belong to is available on the page number 9 of pdf for which link is given below :-

https://jeemain.nta.nic.in/webinfo2021/File/GetFile?FileId=5&LangId=P

Thank you