I've yet to notice anything and I'm pretty old, but I also look much younger than I am, so I'm probably not a good data point. I think attitude plays a huge role here. I don't act like I know it all or have nothing to learn because I'm relatively new to development (officially), having done QA before that. If you're curious and willing to learn, it's unlikely that you'll written off as inflexible and closed minded. (AKA, "age is a state of mind.")

Regarding the article, I wish it had some actual empirical evidence to back its claims.