This behaviour is not uncommon in aging dogs. In many cases, it's an early sign of senility. Put another way, he may be becoming a grumpy old dog. If this is the case, medications may be helpful for dogs with senility.
However, it is also possible his growling could be due to a medical condition, such as arthritis. In these cases, the pain may be exacerbated when he's touched. If the growling is a new behaviour, have your dog examined by a vet.
If the growling is determined to be a behavioural issue and the behaviour is new, chances are you didn't have to train it out of him years ago. Starting to do so now may be difficult, but not impossible. However, if you successfully trained him not to growl at strangers when he was younger, then your task should be less challenging. In either case, reward training, disruption techniques and halter training can work well. Be patient and consistent. Contrary to popular belief, you can teach an old dog new tricks.
