Well I got the 1851 census which just my luck was on two pages and it records a William as 12 so born 1839, Alexander 1841, Daniel/David 1848. If this is the correct one they had William prior to their marriage in 1840 in Dalkeith. Still not sure about this William Snr who was born in Falkirk as I haven't any evidence that Elizabeth Storrie ever moved from the Dalkeith as her parents and her daughter Helen Bolton lived there. William from Falkirk born 1806 parents were Alexander Davidson and Janet Storrie.
On the 1861 census for William Davidson a Alex Hutchison further down on the census seems to be the same squiggle and his wife underneath is 59 so if it was a 22 her husband is 37 years her junior. The scribes 2 seems quite distinctive as does his 3 but his 5's vary. So not sure what to think.
Do we agree that there are two William's born 1806 one in Falkirk with parents Alexander and Janet nee Storrie. A William 1804 according to his death certificate parents William and Elizabeth nee Storrie
That's all I have found
Eileen