Justin Bieber went all the way to England to celebrate his 19th birthday because the drinking age over there is 18.  But there was a problem:  Justin hangs with people who are still under THAT drinking age, too.   Like 14-year-old Jaden Smith – Will Smith’s son.

Less than an hour later, everybody left because Jaden tried to get in and the club wouldn't let him.  Justin Tweeted,  "Worst birthday."

And a spokesman for the club said,  "We are very sorry, and understand it's his birthday, but our hands are tied with local authorities and rules we need to follow as [a] club to keep our license.  We clearly didn't want to give him the 'worst birthday.'  He is a friend and previously was always welcomed with open arms."

After they left, Justin and his peeps went to McDonald's . . . then back to his hotel at about 3:00 A.M.