There are so many ways in which you can lose whatever relevance you had in the world.
It can be taken from you, by force, from others. That happens early, when it still has value. You would notice.
It can also wander away without you realizing it. You while away the days, keeping to your domain, while whatever influence or knowledge you had becomes less important, friends drift away, few remain behind you other than those who had similar trouble holding on.
Or, saddest of all, your can hold on to it for ages. You are still what you were, in your own back alley, while others build a new world just outside your borders, a world which continues to expand and accrete and compound without your knowledge until, a decade or so later, you are still holding on to your tiny speck of importance and your outdated code, neither of which has any relevance on this new environment.
That's Mr. Six. He was a gangster, used to settling problems with his code of honor and stern talking-tos and the inevitable back-alley fight. When his erratic son disappears, Mr. Six and his tools are inadequate to deal with the brave new world of impossibly rich kleptocrats and their well-insulated princelings. Too proud to ask for help, just sticking to what is exactly within his means or what he is owed, he tries. He brings along his band of old timers, small enough to fit around a tiny back-alley restaurant table and, like the restaurant, colorful, noisy and unpolished.
Nostalgia and its core cast, though, is most of what Mr. Six has going for it. Your enjoyment of the movie will depend on how much you get out of those two. The veterans need to face off against wooden young models and clunky camera angles. They convince you to stick around for a script that meanders before turning cloying, that backpedals from a brief critical look at its central character to lionize him, that abandons the personal scale for flash.
They almost carry the day.