In josaac admission process I have ST certificate of 12 year and it is only my source for verification and unable to make digital certificate so can it is valid or not
Hello,
caste certificate is valid forever. so you can use it for verification. There won't be any issue. if you have any documents which has crossed it's validity period then better to make it before the date of document verification.
You don't have to re-new caste certificate for any registration/verification process. Hold original documents and provide xerox copy or additional copy of the document.
Hope it helps!