LA Clippers Boss Donald Sterling's Gf, V. Stiviano 31yrs Fooled Him She Is 21yrs- Birthday Photos.

This is quite funny- 10 years difference should be noticeable even down they, how did he get so fooled to believing she is just 21yrs? Anyway, when you're Donald Sterling's sugar baby, you can have your cake and eat it too -- V. Stiviano celebrated her birthday last October with a giant cake that said "HAPPY 21st!" ... even though she was actually turning 31. TMZ has released the photos.

The party took place at a restaurant inside the Staples Center -- and you can tell from the pics, these were happier times for Sterling ... possibly happier because he thought he was dating a woman 10 years younger than she actually was.

The cake says 21, but According to TMZ the court docs reads ... Stiviano's actually 31.

Sources close to V. Stiviano tell TMZ, she has notoriously lied about her age for years -- so it's not a stretch to think Sterling believed his sidepiece was barely legal.

Not like Sterling would be able to tell the difference anyway.