I suspect there are a couple of reasons - especially in the newer/startup space: * Salary. Older employees are more experienced, but, just as importantly, they've already job-hopped a bit, so their base is a lot higher. And they've probably a lot more personal financial responsibilities. All told, they're unlikely to go for the same salary as a new grad. * Interview process. Anecdotal experience, but, the interview p…
Some of those points are actually age discriminatory. For example, why assume that an older person should earn more than a younger person? Instead, it's better to think about paying people in proportion to the value that they provide to the company. I understand that many startups simply do not have the cash required to pay a high base salary. But, that's what equity compensation is for.
The younger candidate might be inexperienced but a fast learner; the older candidate might have a lot of experience, but might be reluctant to adopt the companies coding practices...
There’s no way to know which of them is going to provide more value in the long term; but you do know that one of them expects a significantly higher salary.