Confusion between these words is due to spelling and pronunciation. Linage is a word of two syllables (LIE-nij) meaning the number of printed lines covered by an article, story, advertisement, or the like and also the amount charged or received for each printed line. It is always pronounced in two syllables but may also be spelled lineage, a word preferably reserved to mean "ancestry" or "line of descendants." In this meaning, the word (however spelled) is pronounced in three syllables (LIN-e-ij)."The linage in this issue of our magazine is down by 10 percent from last month." "She tried to trace her lineage to early settlers in Jamestown, Virginia."
Dictionary of problem words and expressions. Harry Shaw. 1975.