Time bar to file a loan recovery auit

I lent money to a relative in 2001. There is no loan agreement but an email where he has accepted the amount and has said he will return when suitable. After that, I have no written proof of asking the money back from him. However, in 2018, can I send him a notice for demand of payment of my loan? Will I be entitled to claim any interest? Can I file a suit against him after all these years?