Spring lamb is from six to eight weeks old; yearling is one year old.
"Ontario Teachers' Manuals: Household Management"
Ministry of Education
Right round on his pins as nimble as a yearling the old red went, and catching the buffel between the forelegs, he heaved him up and sent him with a thud on to his side.
"Tales from the Veld"
Ernest Glanville
His altar stands by yonder plane And there the shepherds bring, Toiling up from the fields below, Each day an offering, A lamb or else a yearling kid, A bud-horned lusty fellow, Great cheeses, grapes, or bursting figs, Or apples red and yellow, Or melons ripened in the sun A foot from end to end.
"A Legend of Old Persia and Other Poems"
A. B. S. Tennyson