Anyone who thinks senescence is not a "Natural Occurrence" needs to listen to "Dust in the Wind" by Kansas
Senescence is inevitable. Cannabis is an annual plant in its native climate(s). When senescence takes place in a plant can vary from strain to strain and from plant to plant and is directly affected by its environment.
Will your plants start dropping their leaves in another 14 days of feeding it just water? Depends on the average flowering time of the plant. But, The plant will most certainly suffer from senescence before it reaches the end of its life.
This isn't directed at you, this is just a few thoughts based on the posts....
Drug cannabis is sort of a unique plant in that there is certainly a harvest window of peak ripeness where cannabinoids and terpenes are lets say optimal for the end user. Anyone who has harvested early or late knows that missing said harvest window leads to a less than optimal user experience. I do think the cannabinoid makeup in the flowers tends to degrade (or change) when plants are taken too long so in that respect senescence certainly exists. I've also noticed that plants don't feed as much as they approach that harvest window too - maybe another sign of senescence.
I think it's important to acknowledge the fact that senescence and premature leaf drop are different things. Fading colors and senescence can be different things as well. I think the signs of senescence can be subtle for hydro growers and sometimes very pronounced for organic growers. It should be noted though that light intensity, moisture levels, and the essential elements available to the plant a couple weeks out from harvest can greatly affect the 'signs' of senescence.
So, I don't think flowering plants always show their age with their leaves but rather their age can be seen in their flowers. When flowers start to get that swollen, dull, ripe look, that's the plant on it's way out. However, one could easily keep that plant alive and healthy for God knows how long by continuing to feed and water it regularly. I think taking a 60 day strain to 120 days is absolutely possible (I've taken one to day 90) but the smoke would be garbage.