are you talking vegging a plant as long as you can before you flower it? or just keep it in veg.. the person i got my first clones from had a 2 year old mother and a 2 1/2 year old mother... but as far as just continously growing a plant to flower... well... i dont know that.. probably as long as you had room and lights and temps and nutes to keep it going... eventually i think it would peak out tho...