Apparently the median age at which founders start "billion dollar businesses" is 34 [0] (the same article references a HBR study that says that mentions an age of 45 for "successful" entrepreneurs). That would also generally correlate to an age where one's peers have ongoing obligations (financial, family).
Only circular if the stats are only from within the YC ecosystem, but I believe the stats mentioned are across the entire startup ecosystem. If true, it would actually support the argument that YC does discriminate for reasons that are not supported by the evidence outside of their ecosystem. If 45 year olds represent the most successful entrepreneurs, why are they targeting inexperienced 22 year olds?
Having your team be cross-generational absolutely works. An age gap between co-founders is much more challenging, as it can create a whole host of expectation and alignment issues.
This is where the whole unconsious bias can be a world of crap comes up. Does requiring relocation discriminate against older people? Absolutely. Does highly favoring multiple cofounders discriminate against older people? Yep. But there are perfectly valid reasons to favor these properties that have nothing to do with age. That doesn't make it discriminatory, it makes it a bad fit for old people (myself included). So instead of trying to fit your square peg into YC's round hole, go find money elsewhere.
> An established bias against solo founders
And it is an age discriminator.
It gets a lot harder to get a team together after a certain age. Peers already have obligations.