So here's my take from a python lover that works with old MS technology (ASP in my case).
It all depends. There's nothing wrong with working with an older technology when you have to. Not everything is state of the art and it's good to understand that developing from a blank canvas is nothing like developing on a legacy system. It's humbling to think that at one point, the author of the system you will be working on sat down and thought about how wonderful their new baby would be too.
That being said, it's draining to work with dead technology. It doesn't matter how wonderful the project is, you can't escape that nagging feeling that every minute you spend in the dead tech is a minute you're not spending learning the new tech, and that you're falling ever so slightly behind.
My level of python knowledge hasn't improved as much as it should have since I began learning it back in 03 ish. Since then, with django and others that language has exploded, while I have plateaued. This is because 80% of my working hours are spent in dead technologies.
It's something to ponder as you make your decision, but I'd need more information to point you in a specific direction.