Seems most people overvalue domain age.
I've bought brand new domains, thrown up content, and had been fully indexed in less than a week.
I've also done huge overhauls (content change, site redesign, etc) to well-ranked websites and they've fallen off the radar for months despite my efforts. I've bought older domains that feel like I just bought a new domain that'd never been indexed suddenly. Or sometimes everything just works out without skipping a beat.
And sometimes a brand new domain takes three months to get indexed.
In the end, you wait. Or you're lucky and don't have to. But where you sit at the six month mark has mostly due with you, not the age of your domain or whether you used hyphens or underscores in your URL. The most valuable decision is to just buy something and start developing it. Either way, you're paying the Google time toll, so start now rather than later. You don't need the validation of forum warriors to buy a domain.