14 Year old lab suddenly loss use of back legs

We have a much loved family black lab Ben. He has previously had a hip replacement when he was about 3 years old after being hit by a car.
Today when taking him for a walk around the block he suddenly loss use of his back legs. We had only taken him about 100 metres down the drive way.
When his back legs gave way and he was unable to hold his weight.
He is still happy and really wants to get up and follow us around the house but he is unable to lift himself up and walk over.
Is this this old age catching up to him?
He doesnt seem to be in any pain.
We are going to take him to the vet tomorrow morning. Is there anything that we can do to help him now???????

I am no expert so I am not going to be giving advice here. Just wanted to wish you and your lab all the best. Also keep in mind that most dogs have very high pain tolerances, which means that even if he doesn't appear to be in pain there could be discomfort. Don't be disheartened though, there are like harnesses with a frame and wheels that your lab could use. Its like a wheelchair for doggies. I couldn't find a picture to post of what I mean but I will try.