I found a gift certificate in my home dated back to 2009 for a cancer run.though it's very old, will the restaurant accept it?

If there is no expectation date on the back in the fine print or with the Restaurant? Then, I believe they would have to honor it. I doubt they wouldn't. That would be pretty petty.

They might. Best to call

Legally.... probably not. But call & ask.

Maybe. You might want to call the restaurant first.