How old is too old?

It came out just fine I guess, I didn't notice any gelling or anything. It does smell a little old, but that's it. I've used seafoam before and I know that it is some crazy sh*t. My girl and I have an '05 Sentra and an '08 HHR as our DD's, I want to put this stuff to use. Do you think it would F up anything?