Hi Colin,
60+ Oyster cards are not first generation, but that was what the Oyster app called them, same with zip cards. I added my 60+ Oyster to my web account as soon as I got it, perhaps try that rather than doing it through the app or TfL Go.
No, 60+ Oysters cannot have topup added to them. There is no way to tell when you might have to pay or not where different services use the same stations. For example, the 60+ Oyster is not valid on London North Western services from Watford Junction and Bushey, but it is valid on the London Overground Lioness line services. Similar issues apply with Shenfield, Cheshunt and others. There are also places like West Croydon to New Cross Gate where the 60+ is valid on London Overground Windrush line after 0900, but not on Southern until 0930.