ages

I always had the impression that Warren Oates and Loretta Swit were the "older couple" and Peter Fonda and Lara Parker were the "younger couple". That's the way it seems to be portrayed anyway.

And while that is definitely the case with Oates being twelve years older than Fonda, I think it's somewhat amusing that Parker is actually older than Swit. (By only a month, it's true, but their roles in the film seem clearly defined by a somewhat larger age difference.)