I guess I have to be a bit of a contrarian on this topic. I do agree that fishing in general needs to grow as a sport and that, in the long run, younger people have to fill the ranks. A decent blip due to the pandemic has aided that. But when we talk about money to buy tackle, boats, and go on destination fishing trips, most in their 20s, 30s and 40s don't have a lot of that. And a lot of them have even less time with jobs, kids' activities, and other responsibilities.
I am a member of a local multi species club that is growing. We have several younger members, almost none of them with the time to be more than casual contributors. I find the age sweet spot to be 55 up to 75. These are the people that have money, time, and looking for things to do. Most are retired and looking to learn more about fishing, meet new people and get involved in club activities. And they do. We get plenty of volunteers. Of course the effective length of productive membership reduces with advanced age.
I don't think the key to growth is necessarily limited to getting more young people, although that could help down the line. What is important is engagement, communication, education, entertainment, camaraderie, relationship building, and a variety of activities that members of different skill levels can partake in. If a club isn't working to advance all these elements, yes, it will eventually waste away. But providing value to those looking for it, and with the time and money to pursue it, can be an effective way to keep a club vibrant and viable.