A fifty five year old has more track record upon which to form a judgement.
A twenty year old who can't find cofounders is more likely to be a positive outlier than a fifty five year old who can't. There are another thirty-five years of adult people skills there. If a person knows a cofounder would help but eschews finding one, it's not a strong positive signal.
I'm not sure that's true, a 20 year old is among their peers when trying to find a cofounder. I would expect it to be harder for a 55 year old to find a cofounder. I understand judging on not having a cofounder period, but age shouldn't come into it directly.
It's true an older person has more past, but if they were in a different line of work before there is only so much info that can be gained from it. It shouldn't be treated as a negative, at least not any more so than a fresh out of college kid is viewed.
At the end of the day it is quite literally age discrimination when you start making different judgements about the same measures (like presence of cofounder for example) just because of someone's age. To me that is clearly wrong. I don't have a problem with judging on factors that happen to relate to age (again like presence of cofounder), but however a particular person scores on that metric has to be taken at face value, not with reference to age.
No cofounders is a known problem when it comes to YC applications.
Finding a cofounder is not going to be among the hardest problems either will face.
It is not unreasonable to expect significantly greater resourcefulness from a fifty-five year old than a twenty year old when it comes to any particular problem.
A twenty year old who can't find cofounders is more likely to be a positive outlier than a fifty five year old who can't. There are another thirty-five years of adult people skills there. If a person knows a cofounder would help but eschews finding one, it's not a strong positive signal.