I'm 52 and have been interested in SxS for about 8 years now. I was a long time hunter before that. I think that, like with many things, the SxS interest/collecting bug hits at a different point in one's life than when one is "young".
You need the hunting experience and background and you need reasonable economic stability.
While most I've run into are similar in age or older then me, I have every confidence that as time passes, new people will join our ranks in the same proportions from the hunting communities as in the past.
Part of that is the openness with which we welcome newcomers, or do we conduct ourselves with an attitude of scorn for those who haven't learned as much.
My personal experience suggests to me that most SxS enthusiasts are interested and willing to share their passion and knowledge with anyone who shows genuine interest and with that attitude I believe many will be enticed into joining our ranks.