'AH' serial prefix indicates manufacture in 1971.
"AU" prefix indicates 1980
No sn data for that model I can find.
That should be 1975
By model and serial number. Go to proofhouse.com
1912
1911
2006
1871
1910
probably WW1 era.................
1919
Just saw a site saying a serial number 88000 was manufactured in 1916. So it may give ya an idea.