YouTube is growing like a startup — these two charts show the 12-year-old site's stunning surge (GOOGL, FB)

Susan Wojcicki

By the standards of the tech industry, 12-year-old YouTube is middle aged. But lately, it's been growing like a newborn.

The value the streaming video site is delivering to marketers in terms of ad impressions and traffic to their sites is surging. That's paying off in a big way for the Google-owned service; ad spending on YouTube is ballooning.

YouTube is benefitting from having one of the more popular mobile apps, said Andy Taylor, an associate director of research at Merkle, a digital advertising research firm.

"People are increasingly using YouTube as traffic shifts over to mobile devices," he said.

These charts, based on a report on the ad industry Merkle released Friday, illustrate what's going on.

Advertisers are seeing a huge pick up in traffic sent their way from YouTube. In the second quarter, outbound traffic from the streaming video giant nearly quadrupled from the same period last year, growing far faster than from any of the other major social media sites.

Growth in outbound traffic from social sites to marketers in the second quarter 2018, according to Merkle

But marketers are also seeing a big uptick in the number of ad impressions they're getting on YouTube itself. They more than tripled in the just-completed period from the second quarter last year. That helped push advertising spending on the video site up well more than double that seen in the second quarter last year.

Those are even faster growth rates than seen by Instagram, Facebook's photo-sharing service that's five years younger than YouTube.

YouTube advertising growth in the second quarter 2018, according to Merkle