i have one question..
in 2011 bitcoins per 50,000 to 500,000 we spent for nothing, just pranking and stuff...
if one person kept 50,000 bitcoins in his account from 2011 up till now,
would the bitcoins still be valid for transactions?
Yes, validity of bitcoin remains viable for as long as you have the private keys of your wallet secured with you, if your private keys get compromised then anyone can transact with your wallet and then your coins will be gone for ever and there is also not any other way to reverse your transaction.