As a relatively new member and 31 year old (and current high school teacher), I see a few things that may be misconceptions and possible solutions:
#1- I think plenty of young people are engaged in fishing- particularly bass fishing and fly fishing. We need to meet them in there world instead of expecting them to visit ours. So I don't think young people fishing is the issue. I think they engage with groups differently these days. They are still in the outdoors..
#2- I think this forum is incredibly active and full of members who are willing to share information and knowledge. It's one of the reasons I have stayed active online even if I don't make it to in person events because I live in this city. Geographic barrier. This should be a huge draw. How can we get younger people to join this active group?
#3- I would love to see ISA increase their social media presence (for good or bad its a part of young people's lives who have grown up with it.) Social media is older than a student in high school today. They haven't grown up in a world without it. Personally, I find the fishing community on instagram to be huge (bass fishing, fly tying, etc.). Its where I find most of my fly patterns. I don't think ISA has an instagram account? Additionally, as a high school teacher I can vouch that nearly no high school student uses facebook or instagram. It's all about tik tok.
#4- I see very few if no women on these forums. Maybe I'm wrong here though.