Age please

I would like to have the age of this gas furnace please it look more than 20yrs old
Olsen duo-matic
M/N BDS-160
S/N 01824-BDEN

Thank Jeannot

Formally W.H. Olsen Manufacturing Co. Ltd. tilbury ON. Look at the Serial Numbers, Prefix is the Year, the letters and years roll over again, E=1963 H=1966 L=1969 O=1972 S=1975 V=1978 A=1980 D=1983 G=1986 J=1989 Fill in the letters and years . Call (519) 627-0791 Ask for John Crozier

DMO Industries Wallaceaburg ON. Now Olson Technology INc. (519) 627-0791 Serial Numbers, Final letter indicates Year L=1991 M=1992, etc.