It's not necessarily a year. I've heard generally more like eight or nine months, maybe more, maybe (with a lot of luck) a little less depending on the type of site, the inbound link profile, and other factors.
And it seems to be query-dependent. Meaning the site can rank well for less-competitive search phrases much earlier than it will rank for more-competitive phrases.
There are some who swear they've got some "secret sauce" that allows them to bypass the aging delay entirely. I haven't had reason to launch a new site in the past year that I urgently needed to rank well right out of the box so I haven't tested any of these alleged delay-busting techniques myself, though.
And just as a by the way, META tags aren't really a key to good rankings. There are all sorts of factors that figure in to it, but the description and keywords tags aren't among them.
But, in a general sense, yes, it works generally as you describe. One day you're nowhere for the popular phrases you wanted to rank well for, and the next, BOOM there you are.
You might appear to bounce around for a few weeks as the changes propagate around all the Google datacenters, but that doesn't mean your actual ranking is changing, just that the ranking you observe is different due to data synchronization issues across multiple datacenters.
Does that help?