25, and live in SF. No drivers license. Well I had one, but it had expired and I never bothered renewing. I've only personally had to drive a car once in the last 4 years. I recently took a job in the Peninsula, where my commute is now Lyft -> Caltrain -> Lyft, which given the cost of parking in my building turns out to still be cheaper than owning a car - this might be an equation unique to SF.
The only downside of not having a license is getting into bars. Bartenders don't like expired ids and I've been looking into getting a new one.