About eight years and a bit
I would put it at 16 1/3 yrs. With normal production taking half of the machine time. Late shift to work on the Kickstarter. Or maybe 12 1/4
14 machines at 7 months working 3 shifts is 24.5 years of one machine working one shift a day. If the machine runs one shift a day for normal production then two shifts are available for kickstarter. This gives 12.25 years.