Yes Steve, it is a memorial rather than graves and tombstones. 
The following men have "age unknown", but I have been able to find what appears to be their birth year, according to the 1911 Census, when the 1st Battalion was in the district of Medway (at Chatham), and the 2nd Battalion was in the "County" of "Overseas Military" (at Pretoria)
Service No   Birth   Name
4622   1878   MORRIS, FREDERICK, F 
6212   1882   SYKES, ALFRED JOHN, A J 
6228   1878   SMITH, ERNEST WILLIAM, E W 
6269   1889   HANDS, JOHN, J 
6513   1881   HOOPER, EDGAR CHARLES, E C 
6833   1879   MORTIN, ERNEST, E 
7080   1888   GARDNER, JOHN, J 
7813   1891   ROGERS, EDWARD, E 
7827   1889   DYKES, THOMAS, T     
7885   1878   ALLEN, THOMAS WILLIAM, T W     
7924   1886   PRICE, WILLIAM ARTHUR, W A 
8061   1886   INSKIP, ROBERT, R 
8196   1892   O'CONNOR, THOMAS, T 
8234   1884   JORDAN, GEORGE OSCAR, G O 
8292   1872   LYNCH, HUGH, H 
8463   1890   ROGERS, FREDERICK, F 
8553   1886   LEWIS, EDWARD JOHN, E J 
8669   1889   COLE, HARRY, H     
8718   1888   NICHOLLS, FREDERICK, F 
8740   1885   HOWCROFT, HENRY, H 
9019   1884   WESTON, HERBERT, H 
9124   1883   PACKHAM, CHARLES ALFRED, C A 
9255   1886   MOSS, CHARLES HENRY, C H 
9390   1889   SCOTT, WALTER WILLIAM, W W 
9485   1889   YEND, JAMES, J 
9668   1886   GOLDSMITH, GEORGE, G 
9857   1889   MAYERSBETH, ROBERT, R 
10046   1872   KYLE, ALEXANDER WILLIAM, A W