Being really young is a good story – except that by 20, it invites comparisons to Stripe's 19-year-old founder.
Being really old is a good story – everyone likes to see someone 60+ still fighting[developing], especially because there is a pervasive fear of age discrimination here.
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EDIT: I 100% guarantee that even if this project is not successful, if these fellows continue plugging away in the industry, they are going to ship something really awesome.
If it sucks “they’re just 20” If it’s interesting, they’re precocious
imho if you’re using age as downside protection you’ve already lost