Yep, the lack of professional courtesy evident in things like asking someone to write an API from scratch and then abandoning any communication with that candidate seems to be a hallmark of the 20 something tech dweeb. And sadly this behavior is now routine. It also speaks to a larger red flag - namely that the company is letting someone so short on professionalism represent the company. The sad thing is that this is so common. Its not just limited to the 20 something developer but also the clueless HR flunkie/recruiters. The upside is that you usually spot these things quite early and can decline to pursue these things further.

There are no shortage of companies that need someone your age who have been around the block and can bring professionalism in addition to a wealth of experience. Don't sell yourself short. Even if they called you back after a month of ignoring you would you really want to work for them? Probably not. Generally ding dongs like that are only capable of hiring other ding dongs(confirmation bias), hold out for working with adults. You age is an asset not liability.