I think the main difference is that the more experience (and age, if correlated) you have, the more accurately you can judge whether or not (A) an idea is brill

I think the main difference is that the more experience (and age, if correlated) you have, the more accurately you can judge whether or not (A) an idea is brilliant, and (B) whether you have, or can hire for, the skills to execute it successfully. I actually think of them as 3 separate things, not 2. - Some people have lots of ideas, many of them terrible. - Some people have the ability to evaluate whether an idea is good or not. - Some people have the abilities to execute ideas, good or bad. People can have [0,3] of these, but #2 is the rarest in my experience. And if you do have all 3, go do whatever you want, because we'll probably end up reading about you in the news soon enough.