I do exactly the same thing. Stage in random kitchens just for something to do in my massive amount of free time. I have worked fine dine (mostly), Korean sushi, Italian, French-inspired American, Indian, Chinese, Diners, Hotels, you name it. You have to find a chef-owner, or an owner with a chef that doesn't mind having an extra hand in the kitchen. I don't do dishes, but i'll grab a mop, broom, wipe-down a station, move dish through during prep to keep things humming along - whatever anyone that works there does, I do. This is a really big pay-off for the brigade after service, because everything needs to be cleaned, deck brush/mop, trash, fryer, flat top... the standard list... If you start working prep in a kitchen - fly through service and are still there cleaning up and closing with the brigade - you get instant respect.
You also set the tone and expectation of all others that come to stage after you. I've seen cooks melt under pressure before service even started. I've seen them walk right by puddles and spills and not even think to grab a mop. I've seen them stand around and either do nothing, or want to spend the day taking pictures with their damn phone, or texting on it. Or they get frustrated when they get the 500 oysters to clean or oranges to supreme.
You are my age, so I'm sure any of what I just said is obvious - point is that you show up with your two knives and peeler - you grab a board and find a station - and people will be more than happy to throw their list at you. Then work cold or dessert during service, help plate, whatever. All of the sudden everyone is cheering and happy when you show up and they really do miss you when you're not there to take just a little bit of load off their day.
I am 100% for you going out there and doing it. Your feet, legs, back and everything else will remind you that you're not 20 anymore. It will suck to realize 16 hours is really 16 hours... but it's totally worth it. I love seeing and working with the cooks and chefs. Love the FOH people, the whole lot of it. If it made money I'd do it for a living.
You have to find a chef/owner gig because commercial/chain places are either liability limited or not worth working in to begin with. I have turned-down jobs at every kitchen I have ever worked in. Not because i am a master chef - but because I have the same work ethic, passion and motivation that i did in my 20's.
You need to do this man - it is very theraputic! I have a collection of house-issued aprons and coats that chefs have given me or do not want back from me, so i can return and work again for them whenever I want to. It is a good feeling. I've been called to assist overruns, whack weeds and cover gaps. Just me, my bain of spoons, spats and knives and a little passion. (no talent but a lot of passion)
The cooks think we're nuts for wanting to be in their hell for free - but what they don't realize is that I don't see that same dedication, commitment and passion with the fat assholes I work with each day. Working with kids that have the same backbone we did at 20-something is worth every minute of my free time.