Could you please tell me if Khums has to be taken out on old clothes that have not been worn for more than a year?

For example, I bought clothes 5 years ago and used to wear them regularly, but its been over a year I haven't worn them. Do we take out Khums on these clothes?

Yes there is khums on the clothe since one year has passed. Ask for the current market value of the clothes. Divide the value into 5 and 1 is the khums