N.O.S. the link
http://www.our-families.info/famtree/individual.php?pid=I12418&ged=Osborne.ged
Its a long shot but the birth date of his father would fit nicely.
Another note when dealing with units or regiments from WW1, because of the high rate of attrition, many units ceased to exist and people were amalgamated into other regiments/units. One person could have served with, for example, OxonBucks Light Infantry, Somerset Yeomanry etc,etc. So he may not have started his army life in the Norfolks. Usually a web search , starting with the Norfolks will tell you what you need to know. A Roll of Honour for that particular county's regiment gives a lot more info, nost libraries are accomodating if you ring them up, they will have a look for you.