skribs
Grandmaster
For a 12 year old to match a fully grown man, especially one with years of martial arts experience, the kid would need remarkable technique - and no, a grey belt should not lead you to expect that level of expertise. It typically takes a kid about 6 months to reach their grey belt. That's about how long it takes an adult white belt to earn their first stripe on average.
This was a gray+black, which I think is going to be closer to a couple years than a couple of months. One rule of thumb I saw online was that each kid belt is roughly equal to one adult stripe. I'm not sure how widespread that opinion is. Nor am I sure if that means "Gray = 1 stripe, yellow = 2 stripe" or if it means "gray + white = 1 stripe, gray = 2 stripe, gray + black = 3 stripe, yellow + white = 4 stripe..."Expect that they might have the skills of a white belt with a stripe or two or three, but that they are still kids.
I'm not trying to win the match, I'm trying to match the level, at least as best I can. I'm aiming to provide the right amount of intensity that, at my skill level, it can be a 50/50 game. Against the other white belts around my size that means going 100%. Against the white belts that are much older (such as one guy in his 60s) or some unathletic folks we have, that means giving less. Against the guys that are way bigger or better than me, it means giving 100% and hoping that they scale back so it's fair.Aim for pretty much no intensity at all. You're an adult rolling with a child and it's a learning experience not a tournament. Just relax and try to move as technically as you can and use as little of your size and strength and athleticism as you can. If you happen to end up in a match with a wunderkind who has the skills to give you problems despite your size advantage, then take them as an inspiration. Imitate the way they move through positions rather than increasing the intensity in order to "win" the match.
I also do try and match the temperament of my opponents when they are better than me. When my professor or one of the purple belts is flow rolling with me, I'm not trying to beat them. I'm trying to make the right decisions. When they give me the time to work incrementally on advancing or recovering position, I try to do that.