Hi Francois:
Of 15 Robert Aitken births in Scotland 1906,
http://www.scotlandspeople.gov.uk/welcome.aspx there is only 1 listed for Renfrew. You can view the details by buying credits online for ScotlandsPeople which holds official BMD, census, etc. This record would provide address of birth, parents' names, occupations, date of marriage, if applicable.
https://familysearch.org/search allows records searching for Ancestry, a membership service and shows multiple Robert Aitken listings of Scottish births. By entering only Robert Aitken, born Scotland from 1906 to 1906 this and many others surfaced.
Name: Robert Aitken
Event Type: Burial
Event Date: 1961
Event Place: Galston, , East Ayrshire, Scotland
Photograph Included: Yes
Birth Date: 29 Aug 1906
Death Date: 02 Feb 1961
Affiliate Record Identifier: 128654274
Cemetery: Galston Cemetery
Robert Aitken
United Kingdom, Merchant Navy Seamen Records 1835-1941
Name: Robert Aitken
Event Type: Military Service
Event Year Range: 1921-1941
Event Place: United Kingdom
Birth Year: 1906
There are also many records listed for Robert Aitken born in 1906 who emigrated.
Depending on where you live, your local public library may provide free access to Ancestry, which would allow you to explore these further without cost.
Hope this helps some,
Frances
John Kelly (b 22 Sep 1897) eldest child of John Kelly & Christina Lipsett Kelly of Glasgow