You do realize, don't you, l4l, that what you sign up for is Gmail.
You sign in to Gmail first.
Then when you're on YouTube and it says 'sign in', all you do is click the 'sign in' link and you're automatically able to see the video because Gmail already knows you're over 18.
(It's not uncommon for many sites, like The Witcher 3's site, to ask you to confirm your age before you're able to view it, though how they determine you're not telling a big one is beyond me.
)
Gmail is more than another site, as you must know and if you need or want another email program it is handy.
I'm not sure why you'd be wary of it because you don't have to 'go visible' or join Google+ or give Gmail any but the most basic information.
(Believe me, I give them nothing over the little I had to to get my Gmail account.)
And as I said, you can clear the cookies and you'll automatically be invisible to Google until you sign in again.
Nonetheless, I understand you might not care to let Google know you're even alive but me, I can't imagine not being able to view things like The Witcher 3...or anything, really, that requires permission...on YouTube.
(Apropos of noting, I'm watching a walkthrough of an adventure game called
Warcraft Adventures: Lord of the Clans that was never released for some reason but here it is on YouTube, on what appears to be a Russian's channel.
So far, it's pretty good, the background art is beautiful and I do like the idea of having an Orc for the hero!)
Your call, of course!
Gil.