what if your idea is an algorithm that can take a photo of someone and tell your their age? If you have a detailed understanding of how the algorithm will work (and what won't) and you have proved it will work, someone can steal that? Is that OK?

I agree with the "ideas are nothing without execution" but I feel like this applies largely to the consumer web/apps field. There are a lot of other 'ideas' that have taken years (maybe even a lifetime) of research and work.