Trying to get contributions from older generations is tough, but would likely provide the best advice. I need to find a few media sources to submit to that target this age group.
I think getting advice is the hook to get people to the site. Once you get some valuable advice, the theory is that some of those people will be inclined to participate.
I'd think about this approach:
1. Seeding this with advice from people you trust. Don't even get them to register - just get the advice and input it yourself
2. Aggregate advice into posts e.g. "Top 10 lessons for peopel in their 40s from the future"
3. Share / pay to promote those posts on Facebook
4. Profit (?)