I have German shepherd male 11 years old he start have problem we back legs to walk and stop eat can you please tell what is the problem what I can do thanks

I know when an animal stops earing there very sick at that age he's probably ready to be put down you don't want him to suffer I had a Shepard Rottweiler mix he made it to16 but he suffered in the end he ate until the nite he woke me up at q00 am I new he was dying a sat with him lust peten him and loving him until he passed I wish I could have had him put down but it was so late at nite and he ate the whole time but when they stop that's it. I just had my 18 year old cat put down at spa there great but he's not earing

Take to Vet, he has hip dispacia?