See: https://tfl.gov.uk/fares/free-and-discounted-travel/60-plus-oyster-photocard
Regardless of what the website does or doesn’t seem to allow, the advice here is “You can’t add credit to your 60+ London Oyster photocard to pay as you go.”
As Mike says, the 60+ card is valid on the advertised services and you’ll need to buy another form of ticket for travelling with anyone else.