Here's what they published lately.
Every person on Earth watches nearly one hour of YouTube a month - on average (6 billion hours watched per month). Since it's just over one billion unique users, the average (!) time seems to be around 6 hours / month.
100 hours (4 days+) uploaded to YouTube every minute.
YouTube reaches more US adults aged 18-34 than any cable network (Nielsen).
And mobile makes up close to 40% of the entire viewing time. Factor in that YouTube is available on game consoles, Smart TVs etc.