We have a avocado tree in the backyard thats 25 years old we grew from a seed that seems to be dying or has some sort of disease . Its 25-30 feet high and has dead branches on the top but it has stems and new life at the trunk . the new stems grow leaves then they turn brown! can anyone provide any advice ?

I used to water this plant as a 12 yr old kid for my mother so im very interested in helping her