Yes your plant is ready enough.
It is not senescence, this is burning due to over fertilization or a build up of nutrient salts in the substrate.
Since you are growing in coco, have you been getting 10-15% run off each and every time you irrigate??
Salt build up makes sense if you have not fertigated, the plant drawing on what is already there and being burned would indicate an excess of salts in the coco from which it has been drawing moisture.
Excessive phosphorous could also be a contributing factor, a bloom fertilizer with a NPK ratio of 3-12-6 aint ideal.