Most software engineering work is far from Nobel prizes work, or even research. In an organization, more than 50% of the workers are basically intellectual assembly line workers. In the remaining people, a few will specialize on each technology, a few will specialize on company-specific stuff, a few on the build system, a few on talking with marketing/business. But the majority of people are doing a medium-intensity job that doesn't require much creativity or genuis.

There's absolutely nothing wrong with that or those people. But this means that your output will be a function of your experience and energy. When you're older and inexperienced, you're compared against people that have the same experience but (statistically) more energy. Thus it is the logical choice to prioritize the younger people.

If you're older, you either have to have something new grads don't, or the supply has to be so limited that they're ready to take you too. If you don't have an answer to "why should we hire you over a young graduate?", this means that you don't understand the basis of the business, which is a heavy red flag for an employer.