note: Was listed as oldest ''son'' [http://en.wikisource.org/wiki/Alexander,_William_(1567%3F-1640)_(DNB00)]
Must have been Born prior to 1604 (1590`s?) due to fact brother Sir Andrew was Born in 1590 and is listed as'' second son'' in above citation.

Biographical Summary

"William, styled Lord Alexander. He was born about 1604 and educated at the University of Glasgow, entering there in 1618. He was knighted at Whitehall 22 March 1627, and in March 1628 started with an expedition to colonise Newfoundland, Canada, and New Scotland...

...He was admitted a member of the Privy Council 26 January 1635, and interested himself actively in its proceedings, being a member of many committees. The day after his admission to the Privy Council he received further honour of being appointed an Extraordinary Lord of Session in succession to his father. He did not survive long thereafter, dying in London 18 May 1638. He was buried at Stirling. He married, probably about 1629, Margaret, eldest daughter of William, eleventh Earl of Angus and first Marquess of Douglas. She died 1 January 1660, aged forty-nine."

SOURCE: The Scots peerage, Vol. VIII, page 176-177