Hii Kritika,

Hope you are doing well.

Character certificate older than 6 months is not considered and the admission authority might ask for a fresh one. If they ask you for a fresh one  write an application regarding the certificate within a given period of time.

There is no problem to get a new character certificate. You just have to go to your school from where you have passed 12th and there you have to ask to principal and write an application about it.

In some institutions they might accept the old one, but it's better if you write an application to your authority to get a fresh one. Shouldn't take any risk.

Hopefully this will be helpful.

BEST wishes for future.