This "man" (he was only 15!) enlisted as MARSHALL, and so is mis-filed in the WW1 Service Records (WO 363):

Edward MARCHESELLI of Russell Square, London WC, enlisted with the RGA (Regt No. 1359) in January 1915, declaring age 19y 8m.
He was born in May 1899 - 15y 8m.
His mother MARGUERITE wrote in March 1916, enclosing his Birth Certificate, to ask for his release.
The army replied:
"I am directed to inform you that the age of your son according to attestation is 20 years 10 months: and that is therefore his official age."
Thankfully, someone else saw sense. He was discharged (underage) in May 1916.

Anc****y, MAR, pages 9951-9986