Lindsay LohanLindsay LohanIt's Lindsay Lohan's coming of age... Yep, she's finally reached the big 2-1.

But looking back at this lady's life, you'd be forgiven for thinking she was way older.

So how do you think Linds celebrated this most important of days?

Well, before you get carried away with the idea of a mahoosive party and outrageous antics, we're going to have to disappoint.

Even though she was on a break from her latest stint in rehab, she didn't go back to her old ways.

Last month, Linds checked herself into the Promises rehab centre in Malibu.

But you couldn't expect her to celebrate 21 years in there...

So just what did she do?

Well apparently it was mighty low-key... She hung out with a few friends and family during the day at a Mailbu beach house.

And then in the evening she went out for dinner with a few mates to Katsuya in Brentwood, California.

A source told People: "She came in with a whole bunch of friends, there were like seven of them, and she walked in incognito, super low-key.

"They sat down for some sushi and were just really enjoying themselves. She wasn't really noticed at all and was just happy, in a good mood."

This was a turn-around from her original knees-up she'd planned at Pure nightclub in Las Vegas that was to be open to the public.

"I'm going to milk it because it's a big birthday," Linds had said on The Ellen DeGeneres Show in May.

But the bash was cancelled earlier this month in favour of the more restrained celebrations. Happy birthday, Linds.

Check out her b-day beach action in our picture gallery.