I hear native speakers say “I am average weight “, but you are right, there may be others that are more grammatically correct. I think it is used because you’re still saying « I am + adjective ». There are many, many ways to say the same thing.

1) When I was younger, I didn't USED TO like vegetables. "Used to" is correct, but "I didn't like" is also correct, and probably more common. 2) Once, I was eating a piece of pizza when I realized I had eaten a piece of broccoli. Correct, bravo! 3) I had disliked vegetables throughout my entire life. Past perfect simple because this sentences shows completion.

Both are correct =) "Simultaneous techniques" is a compound noun... a noun that describes another noun. These are very common in English. For example "ice cream, mail box, sunglasses, etc.

1) To be sad - temporary situation 2) To be depressed - (We don't use the preposition "out" after this). To be very sad over a serious situation, or due to a mental problem. 3) To be bummed out - to be disappointed (not as strong as "sad")

Hello, I think your writing is very good. Here are a couple things that I would correct to make it sound even more natural. 1) I had something red in my body. We would say "on my body" if this is on the skin. Otherwise it is internal and would not be visible. 2) Something red on my body and itchy. It sounds more natural to put the adjectives together... "something red and itchy on my body". Or, if you prefer, you could say: "Something red on my body that caused my skin to itch". Lastly, yes, you are right... "quit learning" and "stop learning" are both perfectly natural/correct. =)