Indoor avocado tree leaves turn brown on edges and shrivel up and become brittle, why?

Question

tree is aprox 20 yrs old

Answer 1

Based on the tree's age, my guess is that the soil is getting a buildup of salts. You may want to try deep flushing the plant once a month or so to clear the salt from the roots. You may also want to consider repotting the plant. Here are some other helpful tips for you: https://www.gardeningknowhow.com/edible/fruits/avocado/what-causes-avocado-leaf-burn.htm
https://www.gardeningknowhow.com/plant-problems/environmental/what-causes-brown-edges-on-leaves-of-plant.htm