For 50+, Facebook is a great platform, as you mentioned. Another one that still does well with 50+ is print, either in your daily newspaper, or magazines. It would depend on the behavioral targeting you're looking for, but print readers are typically 50+ and more affluent.

Another word for authentic is believable. Meaning the consumer can believe what the brand is communicating about itself, its products and its culture. Apple appears authentic because they demonstrate how their products simplify life and make it more enjoyable. Honda expresses reliability and fun, and their products are certainly known for reliability. Look at struggling brands, like Sears, who tried to be all things to all people, from Craftsmen tools to Lands End. It was too broad and general, and the market validated it with declining sales.

The best step is to look at things in your everyday life, and figure out what are the pain points, or what can run smoother. Your best chance to get a business idea isn't from something that you know nothing about (for instance, I'm sure there are great ideas to start businesses in aircraft production, but I know nothing about that industry, so I wouldn't know). What's going on in your world that seems like it could be easier? Think about everything you do on a daily basis and look for improvements. Then think through your head what those might look like. If you'd like to chat through this process, let me know!