Removing the apical meristem (growing tip) of any branch or stem permanently terminates it's growth. There is a growth regulator produced in the apical meristem that suppresses lateral growth along that branch or stem, so when it's removed, another growth regulator becomes dominant and stimulates new lateral growth - usually from leaf axils (crotches) along the stem/branch. Right now isn't exactly when you'd expect the most robust growth on your avocado, so be patient - it will happen as days lengthen & the plant wakes up. I can't advise you about whether or not it's safe to fertilize w/o knowing something about how you water. We can talk about that, and I can help you with an easy way to make certain it's safe to fertilize if you wish. Plants cannot grow normally unless all the essential nutrients are available for uptake. When plants are growing in container culture, you shouldn't rely on the soil to provide them, because it can't/won't, so it's very important that you provide them via fertilizer. The question now is, can we safely add fertilizer to the current level of salts in the soil or should we flush those salts from the soil first? Al

Yes, I agree with Jean and Christine. To my eye, the old damage is from cold exposure. My avocado leaves are fairly beaten up from the cold they experienced this Winter, although the damage isn't quite as extensive as on this plant. Secondly, the pot is very large, the soil is indeed overly wet, and the pot is sitting in a driptray with water still visible. At the very least, I would elevate the container so that it does not sit directly in water and continue to wick moisture back up into the rootzone. I would recommend re-potting this Spring, if the plant survives. The new mix should incorporate much more porous, gritty materials, such as perlite, lava rock, pumice, turface, DE, granite, et cetera. Until Spring, be very careful with watering and give the plant as much light as possible. Josh

Well, since there's no big loss if it doesn't work, how about re-potting it in a very well draining mix, and putting it outside for more light. If it's been inside a long time, set it out in the sun slowly, like a couple hours the first day, then back in a shady spot (but still outside) more hours the second and so on over the course of a week or so. That way you'll not shock it or sunburn the leaves. Also, don't fertilize after re-potting until you see new growth, then use a good liquid citrus food at half strength. Avocados don't need a lot of humidity, they like it just fine but they don't NEED it. If they did they would not grow in areas like Southern California, which is basically a desert. So I wouldn't worry about that if I were you. And I would snip off that brown tip just past it and into the green trunk. I've found brown tips like that just keep going unless you cut them off. It might still come back, imo, 50-50% chance.

Babies are very temperamental. Give them as much sun as possible. Once a week maybe too much water. Empty the pan under, if you have one. Let the soil dry completely. They don't like wet feet.