Odd question. I have a 1940s Aga. originally wood-fired but converted to paraffin in the '70s. Although it is unusual for Agas to be so old, especially since they can be bought new as under the traiding name 'Rayburn'.
There is no clear answer, some youngins are old and some oldins are young. Another opinion: At least 80. On the lighter side. This answer was kindly dedicated to Lazarus