Maybe it's an unpopular opinion here.
In reality, young people are less paid than older counterparts in almost every economic sectors for the same skills. I mean that'a known truth! Silicon valley is the opposite? Good for the them.
I think there is 2 strong biases against older founders that might explain the situation:
1) The man is not a programmer and don't have a feeling for high tech stuff. I know founders here in Paris in their forties. They are starting web startups while not even knowing how to connect to wifi! But because they are old and have connections, they get funding! You are telling me in the valley it is the exact opposite? It seems just fair to me!
2) The man is a programmer and a good one. In their forties, you might expect him to make something like 350k and have a good title like CTO or lead developer. Why he will risk everything to start a new company? I can understand why people feels it's odd. Maybe there is a 1:20 odds to make it so he must aim for at least $7m to make any financial sense to him. Or maybe he is not a good programmer.
What? There are quite obviously not as many CTO or "lead developer" positions as there are junior engineering positions. So why are you assuming that everyone that old must have such a great job?