Dear student

Yeah definitely you can use your December issued caste certificate and income certificate for applying scholarship program for sessions 2020-21. In any state caste certificate and income certificate are minimum valid for upto period of six month from the date of issue. So you can use your certificate upto almost may2021. After that usually castes certificate doesn't need renewal because caste doesn't change  but you will have to renew or make new income certificate after its expiration. Usually income certificate is valid for 1 year.

Hope this information helps you

All the best