Why does my 14 year old dog have trouble getting up the stairs?

Probably because he has arthritis.

What does the Vet say? There are many products available for arthritis in dogs.

And of course 14 is like old age for dogs, so he would most likely be slower ( like your grandparents) when was the last time he had a complete check up at the vet ?

My 12 year olg GSD has arthritis and hip dysplaysia. Stairs and uncarpeted floors are tough for him these days. I just had a runner installed on the stairs so he get up them . It takes him a longer but he can still get up. Going down is easier. My vet gave me some pills for the arthitis but he still is slower than his youth.

- and I had a wheelchair ramp put in so my dog can get off the deck and onto the lawn.