Is it too early for the leaves to start dying?

Sometimes it just happens , its a sign of your plant maturing . With that being said not every time this is going to happen its going to be like that but based on what I see its ok . Sometimes older leaves just go yellow for seemingly no reason which is fine its the lower leaves and its just a few . If how ever your plant started to get yellow all over for no reason then I would suggest deficiency's . You can basically pluck these leaves off cause they arent doing anything positive for your plant , the only thing thats doing is making a nice nest for possible invaders to your plant . The only thing I might be able to suggest to you to slow the yellowing like that is to up the calmg dossage to 2ml/l the reason I say that is cause I can see the plants red stalks on the the leaves and main stalk this is a classic signs of calmag deff . This in late stages like you are in now can cause leaves to yellow up , but it would be allllll over and not just a few . So to sum it all up , basically your plant is burning through all the nurtients it can in the medium and in its leaves because its nearing the end of its life cycle I would how ever add more calmg to the mix because your lacking in that department on your plant . I hope this information helps on your journey to the finish line ! Happy Growing!