Hi there

Hope you are doing well

Now  let me go through your question

On 28 September your daughter will become 12 years old (completed)

And

According to AISSE ELIGIBILITY

for sixth class Age Limit- The age of a student should be between 10-12 years, as on March 31, 2021

AISSE form will be released on month of September/October

Thats why your can definitely apply for it

If you want to know more about it check out the link given in below

Eligibility

https://www.google.com/amp/s/school.careers360.com/articles/sainik-school-eligibility-criteria/amp

Other info about it https://school.careers360.com/articles/sainik-school-admission-form

Hope it helps

Thank you