19-year-old "Teen Mom" star Maci Bookout insists she's "grown up" since her infamous beer-bonging photos were taken ... way back when she was 18.
Maci was out with her best friend in NY last night -- and explained, "I was on vacation and Bentley wasn't with me and I was having a beer."
She adds, "It's obviously something I don't do anymore because I've grown up since then."
For the record, Will Ferrell hit the beer-bong in "Old School" when he was 35 ... and he has 3 kids!
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