I have three 21st cards to make, all for the same young man, and this is the first one. I've used the colours from colourQ's current challenge:
And the inspiration has come from this card by Julie Ebersole, guest designer for CASE Study:
And one of the current challenges at Moxie Fab World is to emphasise the negative, featuring in Card Creations, Volume 11.
It was a long time ago, but I don't recall there being anything negative about reaching 21!