They have Living Legends at the National each year. One of the owners has to belong to the NCA. You submit your information, a photo and a statement from your vet that the dog is still alive and the age and there is a designated person to send all this to. Then at the National they read out all the names, those who bring their Newfs to the ceremony are given a medallion and a booklet of all the dogs submitted.
We did this for Gracie the year she was 14. We didn't go that year but someone sent us the medallion and booklet afterwards.
Other than that I don't think the NCA or AKC recognise age in Newfs.