Hi  My Gsd will be 13 in december, still enjoys her walks , likes to play with my young Gsd. eats ok eyesight good, but a bit deaf now, my problem with her is she has got very dirty in the house, as soon as she moves after a sleep she starts to poo, every morning when I get up she has pood, she goes out late at night and I get up about 6,30 am, some days she does it in the back of the car on way to do the horses, she is fed on Arden Grange  so the poo is firm  thank goodness, we never scold her. just pick it up and dispose of it. She always use to eat her poo but has been on AG for months now and she has stopped doing that. Is this just a sign of old age?

I'd say a visit to the vets was in order, how is her hind moment? My initial thoughts are it could be an early sign of CDRM, but maybe that's just because my last boy had it and I'm jumping to conclusions.

My friends doberman bitch of this age was the same, seemed quite shocked to find a poo at her feet, again it was dry so easily popped into the downstairs loo.

It was simply that she no longer had the control of the actual exit.  It usually happened when she got up from lying down which at this age with being a bit stiff took a bit of effort and the result a nugget.

She is never stiff after a walk, in fact today she spotted a hare , the mind is willing but the  body takes a while to catch up. She does bunny hop when she is running, and is always keen to fetch the toy.

Does she ever trip over when turning? Or drag her back feet like the dog in this video?

no, she has no scuff marks on her feet, she is just a bit lower on her back end than she use to be, I use to do agility with her , but stopped that due to being diagnosed with HD but she attended  hydrotherapy for several months and has never had pain again, she gets up into my car ok, I will have a trip to the vet  just to be sure.

My old akita boy used to do this.  He had HD too.  My vet told me that he had just lost the sensation at his back end which was good as he was never in much pain (from the HD),.  Like yours, mine never noticed.  He would stand up and stretch and then notice the poo and then look round, disgusted at us!!lol It was so funny.
I never worried about it and just discretly cleaned it up.
It also happened to another couple of my Large breed dogs but one had arthritis from cruciate ligaments going and the other had CDRM so it's not just a HD thing.

That would make sense as my friends old dobe girl did not have HD (low hip score) but was very stiff and arthritic in the back as she got old.