Maybe I'm an outlier; I'm a 55+ engineer working at a mobile startup. Maybe not; 20% of Google's employees are >55, according to a Kissmetrics chart. But, who knows maybe the 55+ crowd at Google consist of only geniuses and janitors.

I see an old/young tradeoff between pattern recognition and fluid intelligence.

Maybe why some older developers show less enthusiasm for the next really "awesome" idea is that is really isn't that new. Maybe the older developer has already learned the hard way the downside of the Dunning-Kruger affect, where: the more you know, the more you know what you don't know.

On the other side of the coin, maybe older developers have a blind spot towards opportunities that have failed in the past. Because the timing wasn't right. Because the audience wasn't ready or the infrastructure was premature. The secret of a good joke (and startups) is timing.

Perhaps some startups are best structured like a team sport; with both younger players at the peak of their brilliance and with older players that can both play and coach.