This is an excerpt from The Book of Scottish Song (1843) edited by Alexander Whitelaw:
"It Is said that Burns wrote this charming little song on a real incident. A young girl, possessed of some property which would be at her own disposal when she attained majority, was urged by her relations to accept an old and wealthy suitor. This she refused, as her affections were already placed on one whose youth, if not worldly circumstances, was more in accordance with her own-and the song is supposed to express her own feelings on the subject to her favoured lover, and particularly the ardent desire she entertained to reach that age when she would be mistress of herself, and able to prove the sincerity of her attachment. The song is sung to a lively old tune called "The Moudiewort.""
An' O for ane an' twenty, Tam!
And hey, sweet ane an' twenty, Tam!
I'll learn my kin a rattlin' sang,
An' I saw ane an' twenty, Tam.
They snool me sair, and haud me down,
An' gar me look like bluntie, Tam;
But three short years will soon wheel roun',
An' then comes ane an' twenty, Tam.
A glieb o' lan', a claut o' gear,
Was left me by my auntie, Tam;
At kith or kin I need na spier,
An I saw ane an' twenty, Tam.
They'll hae me wed a wealthy coof,
Tho' I mysel' hae plenty, Tam;
But, hear'st thou laddie! there's my loof,
I'm thine at ane an' twenty, Tam!