Sounds like awesome progress and if you're able to hold that kind of speed over that kind of distance I reckon there is zero chance of you embarrassing yourself at a cycle club. Perhaps don't go for the highest race level stuff straight off the bat but tbh it looks like you won't struggle at all.
Yeah, its progressed really well. Up until 5/6 years ago I was always 'sporty' with football and running, but my knees gave in and kids came along and the weight piled on and I was out of breath running up the stairs!
I'm gonna give the club a go, but as you said probably just go out with the intermediate group to start with. Thanks.