How long is a regional pilots career?

You forgot the apostrophe.

To answer your question, nobody knows. Some move on within a year; others are still waiting after 2 decades. With the tremendous uncertainty in the future, go somewhere you can see yourself staying for at least 10 years. You just never know if you'll get stuck at your carrier- the last thing you want to do is go to someplace crappy, intending to use it as a stepping stone, and find yourself there many years later, wondering where you went wrong.