(though irony has it that some mainfraim experts can earn a fortune because nobody has that skill any more while some companies do still need it.)
As for cultural fit; you'll see youngsters in t-shirts getting rejected at bigger corporates, and 'older' developers in suits getting rejected at startups. Not necessarily an age thing on a meta level. (or is the question specifically aimed at employment at startups? In that case, ignore my comment above).