Cloning problems, mother plants too old?

I have two mothers that I have had on 24 hr light for over two years now. The first year I had excellent cloning success using a 45 site power cloner, root tech gel, hormex hormone and bio root and roots within two weeks 4 times in a row. Then on 5th time cloning, failure. The mother plant stems are all purple, stiff, and almost bark like. I have tried cloning several times and I have failed to produce roots.

So my question is, do mother plants turn too hard to clone or has anyone had any experiences like this? Is there any way to get my mother plants back to a healthy cloning state, or should i get new mothers. I am still a noob to cloning a little so any tips or help is appreciated.

They get too woody to clone also they get issues living so long in a pot. Start a new mum every 30 clones or 2-3 months.

Thanks for the tip just got some blue dream seeds going to start a new mother soon!