I have a 12.5 year old Aussie too. And we are having some cognitive/sort of anxiety issues. He paces a lot. Etc. You could try an pet calming formula. I have used a formula that had
L-Tryptophan as the active ingredient and that worked pretty well. I got it at the local pet store but I know it is used for mild anxiety in humans too so health food stores probably carry it. If it doesn't work, at this age I would not hesitate to talk to a vet to rule out other problems and then talk about prescription meds just so he is not in distress. While anxiety meds are not the greatest, in my opinion at this age it is all about comfort.
Dutch Shepherd - Ptygo (Tee-Go) de las Flores