Recovery from daughter by father

Prima facie its a time barred debt unless there is a contract to the effect as to when the debt was repayable and that falls within limitation. If the father is unable to maintain himself comfortably out of his own income, he can seek maintainance from his daughter under s. 125 crpc.

Does it mean if it was not time barred, he could file a suit even without a formal loan agreement?

If he could prove the loan transaction by oral agreement then the claim would have been valid, but the oral agreement needs to be PROVED in the court of law which becomes sometimes quite difficult compared to when the agreement is in writing.