Hello, the last date to apply for April/may 2019 for class 12 in NIOS got over on September 15, 2018. You can go through this link to get all the information about NIOS admission for details - 

https://school.careers360.com/articles/nios-admission

no

the last date to register was 15 sep 2018.

go on the official website for further details.

the online forms were available in September was the late registration with additional fees of 700INR.

and they also have an age limitation.

I hope you are not 15+

All the best.