When you don't get a second interview, follow up by email or phone and just ask what happened. Make it clear that you're not questioning their decision or trying to change anyone's mind - you're just looking for feedback to help you improve your interviewing skills. Not everyone will answer, but some will and you might get enough information to start making some changes.

It's wonderful that you're doing good work, and assuming you want to stay at your current firm, I encourage you to leverage what you're doing in three ways ...

Definitely stay where you are. It's rare to find a manager who gives you expanded responsibilities, stretch assignments, praises your work, and goes in to bat for you to be promoted.

I'd suggest educating them on the perspective of younger workers. Often times bridging generational gaps can be harder from the older to the younger crowd. Giving them some insight into your perspective and those of your peers can be very valuable.