Pros
40-something founders and management team means that they've been there before and have a level of maturity and focus that is rare in startups. CEO cares so deeply about customers, community and employees as opposed to his own ego or riches. Laughter and joy are the most common emotions expressed. Customers LOVE LOVE LOVE Zendesk, even if our product (and people) aren't perfect. When a customer tells us they are leaving for a competitor, we actually help them do it, and treat them with respect and care on their way out. And they often come back when they realize they'be been duped. Nobody in the company is satisfied with any aspect of the product, company, design or culture. This gives us all a sense of "kaizen" (continuous improvement) which is very healthy. Plus the Zen thing is more than a fat Buddha on the website, it's weirdly (and appropriately) weaved throughout our culture. And I get to say curse words all the time and people don't get uncomfortable. The "old timers" who were there at the beginning are very welcoming of newer people which is rare. I could go on and on....
Cons
Just typical fast-growing startup stuff. Growing fast has meant some mediocre hires in key roles which can breed more mediocrity. Sales/marketing culture may over-power original product/engineering/support culture, which is fine, but needs to be effectively managed. Amazing contributors (and there are many) need to realize they are amazing and not feel somehow marginalized.