Back in the midwest where I was raised, the local congregation has a pretty good success rate of keeping the 'young ones'
I do feel this is because most in that area do not go on to college and get stuck in the old school small town mentality,, Most in that area never leave and gain work as
carpet installers/cleaners, janitors, logging industry, etc.
There also seems to be a bit of inbreeding in my old congregation. For example,, there are two huge families that dominate the congregation,,
My family(thank god I live 2000 miles away now) and another family. Needless to say, I am now related to the 'other family' because of many marriages.
I wouldn't be surprised if during a family tree search you would find that my large family and the other large family originated from the same family(yuck!!!)
Here in california, I attended a congregation in Buena park for a short time. There were some young ones, but hardly any beyond the age of 18.
Then you would find some married couples that were in their mid 30's to 40's so there was a gap. Other than myself, there was no one from let's say 20-30 years of age.
I next moved to long beach, attended a local congregation there twice,, it was just young kids and old people,, nobody in between that was my age.
Now I attend an occasional sunday meeting,, Since I work all over SoCal I randomly pick a new hall and attend,, For me it's fun, since I like meeting new people.
At all these other halls,, basically the same thing,, little kids, and older married couples. My guess is the drop out rate is in excess of 80%