Erm. Probably help him correctly set up a software wallet on his phone then send him a certain amount of bitcoin. Not sure why DOGE is an option, knowing that Bitcoin's fees right now isn't even high.
^Of course, if gramps is planning on allocating a decent amount of money to bitcoin/crypto, then probably buy him a Ledger/Trezor.
That's where I planned to send the Doge coins to? He is a trust wallet user and he likes coins like Shiba inu and Doge coin.