birthday wishes for a 21 yrs old friend

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unlike any other b'days, which i tend to just write some wishes and something nice in a birthday card as part of the proceedure, this is a vital part of life when one takes on his first step to adulthood, from 20 to 21 years of age. therefore, i am seriously considering what is not only appriopriate, but something mature and most importantly, impactful, to his life. what do u think i should write in the birthday card? what is the important points to be emphasized? and could anyone write me a sample? thanks.