I've heard of mother plants being alive for over 5 years, pumping out clones the whole time. My guess is that it was very well taken care of and properly pruned.
I've also heard of mothers only surviving long enough to make a couple monocycles. Not good. Probably very poorly taken care of.
But, it all depends on the genotype, environment, stress, epigenetics, and i would wager medium may play a role as well.