Hi Patricia,
The 60+ Oyster card is not a simple thing. It is valid on TfL services from 0900, but non-TfL services from 0930. So someone travelling from Norwood Junction to New Cross Gate at 0900 has to be careful to get an Overground train rather than a Southern one. Outside the zones it’s valid on TfL services* but not non-TfL services, so from Shenfield you can use the Elizabeth line but not Greater Anglia. Obviously these distinctions can’t be decided by the gate pads which is why you can’t add credit to a 60+ Oyster card.
In terms of extension tickets, you can buy those from some stations, or online. You might have to use a named station rather than boundary of zone 6 if buying online. I’m not sure whether you can use e-tickets if you don’t scan them in at the beginning of the journey. The prices will be the standard ticket prices, not the PAYG prices. For Gatwick you can get the PAYG price by getting off at East Croydon and taking the next train once you’ve touched out the 60+ and in with the bank card. If you have a senior railcard then that can be added to an Oyster card and used for East Croydon to Gatwick. St Albans isn’t so easy because there are fewer trains stopping at the boundary station Elstree and Borehamwood. Oyster also isn’t valid at St Albans.
*But not the Elizabeth line between West Drayton and Reading.
