The phrase "old stager" refers to a person who has been doing something for a long time and has a lot of experience in that particular field or activity. Full definition
After all, directors such as Paolo Sorrentino and Matteo Garrone are fixtures on the international circuit, as well as old stager Nanni Moretti. (theguardian.com)
Despite the pro-AV leader, Ed Miliband, having stuck his neck out a few times for the yeses, belligerent turns by grumpy old stagers such as John Reid and David Blunkett have created the impression that the people's party has no interest in giving the people more of a say. (theguardian.com)