The birth date of 1126 seems to be unfounded. The sources given are files of leftovers from Gedcom imports.
Having him die in 1142, at the age of 16, with a wife and two children seems theoretically possible, but unlikely.
The "cousin" page from rootsweb has his birth as "ca 1100", which seems less unlikely.
Are there any real sources around?
Paul Theroff has him dying 1142. My guess for birth is c1090.
http://www.angelfire.com/realm/gotha/gotha/rohan1.html
Complete Peerage says he married after 17 Jun 1119.