I'm not sure "evolution" is on the table for humanity any longer. For one thing, evolutionary pressures don't really exist for humanity, outside of the most undeveloped areas.
Not making it to "breeding age" (feels weird to say that in the context of humans) doesn't really have anything to do with fitness any longer, more just luck.
Add in the fact that we basically already have the ability to manipulate human genes - and I think it's far more likely that we'll just start tinkering with our genetic code deliberately, as opposed to what we think of as evolution