Generally speaking, if they have a Wikipedia entry, then they're considered to be Notable. If they do not have a Wikipedia entry, then we have to ask - "Would they qualify for a Wikipedia entry?" - Then, we have to determine under what criteria they qualify and how are they Notable?
Keep in mind, there are many interesting people in the world who have done many interesting things. This doesn't make them Notable - it just makes them interesting. Notability tends to be something they've done or are doing that would push them into a "famous" zone. First to fly a rocket. First of their gender/race/religion/etc. to own a company in the US. First to hold a particular office. And so on. And the old story about "Fame is Fleeting"? True. What was yesterday's Notables might be old news tomorrow. I've seen Wikipedia pages deleted from time to time as their moment in the sun fades away.
So the bottom line - if you feel you have a potential Notable, explain why you believe they are Notable in a way that makes them different than any other person who has done what they did (or do), why they have achieved the "fame" zone in what they did (or do), and if necessary, why they don't currently have a Wikipedia page but you believe they should have one. It's harder than it sounds, but can be done.