Had alook to see if I could find a birth record for him and in Free BMD Linkhttp://www.freebmd.org.uk/cgi/search.pl
There is a birth registration for a Gerald McEllistrim Brooks Mar 1909 Cardiff 11a 476
Gerald Brooks age 2 is also showing in the 1911 Welsh census
Father Isaiah Brooks miner age 36 b. Glamorgan Mother Julia Brooks age 34 b. Tralee Kerry (wonder if she was Julia McEllistrim) parent married 16 yrs and had 7 children 6 alive in 1911.
Will check to see if there is any record of a McEllistrim/ Brooks marriage.