It depends on the variety in my experience....some can last a few years but some will start to get funky, I say replace it with a cut if your in love with that pheno,
or start beans to throw the dice...
When you start to notice rooting time taking longer and slight lack of growth vigor and a loss of yield with all other variables met; then you should replace the mother.
I'd say a 5gal is way too small for a year old plant and will make her weak towards the end of your year....
Go as big as your area permits for mother plant containers and don't be afraid to prune roots when transplanting and give her lots of foliar action, the mothers love it!