For 1 and 2, I believe you've got the answers from the earlier replies. For 3, 就 usually used to modify the part behind it of it's EARLINESS, QUICKNESS, or LESS NUMBERS to the speaker. In this case, it indicates earliness. It means the speaker thinks the child started painting at a very early age, just since he was a kid. Other examples, 他18岁就结婚了。我今天早上5点就醒了。他去年就开始学汉语了。You can use the structure [age/time/date] + 就…… 了, to express earliness of the part behind 就. Hope that clarifies.

Thanks to everyone for your help. 非常感谢

我從我還是孩子的時候起就開始畫畫了。 1) Why is 還是 in here? Doesn't that mean "or"? Re: 还是 in here means that: you were a child at that time, but now you grow up, you are not a child anymore. 2) What does 起 by itself mean here? I'm used to seeing this as 一起 (together). Re: 起 in here means a time node, i show you an example, 自从我认识她起，我就喜欢她了 means when i saw her in my first eyes, i just loved her. 3) What purpose does 就 serve here, and does the 就 necessitate the 了 at the end? Re: sorry, i do not know how to explain this question

我從我還是孩子的時候起就開始畫畫了。 I began to draw/paint (/ to learn drawing/painting) from my childhool(/ from when I was very young). The Chinese sentence is more commonly said as ' 我从还是个孩子的时候就开始画画了。—— The second 我 is so near to the first so that it is repetitive and redundant and usually is left out. 1) Why is 還是 in here? Doesn't that mean "or"? ------ 还 here in the sentence is an adverb[[please refer to dictionaries for more detailed explanation for the use of 还]], implying a emphatic tone. 2) What does 起 by itself mean here? I'm used to seeing this as 一起 (together). ------- 起 in the sentence can be identified as a verb( and this is the common treatment in grammars by Chinese writers, compare: 从...开始) , but for CFL learners it might as well be regarded as an idiomatic pattern, meaning 'from...', and 起 can often be omitted. 我从还是个孩子的时候就开始画画了。 By the way, some idiomatic patterns, such as 在...上，从...南部，each consists of two words bracing a nominal phrase in between. 3) What purpose does 就 serve here, and does the 就 necessitate the 了 at the end? -------- 就 here is also a modal adverb(same as 还）, and 还...就... is also a common imdiomaic pattern. 了is a modal auxiliary. In some sense you can say it is the prior 就 that causes the appearance of 了 in the sentence end. Please compare: 我_是_从还是个孩子的时候就开始画画的。...就...了 and (...) 是...的 are commenly used idiomatic patterns too.

1) Why is 還是 in here? Doesn't that mean "or"? ”还是“ 还有 "still/just“ 的意思。在这里的话，主要是用来强调他当时只不过是个小孩。 这句话完全可以改成：“我从小时候就开始画画了” 有点类似这两句话的差别： I started painting when I was still a little boy/girl. I started painting from a young age. 2) What does 起 by itself mean here? I'm used to seeing this as 一起 (together). 这里的 “起” 是跟前面的 “从” 连起来的：“从。。。起” 比如，从明天起我要开始锻炼 Starting tomorrow, I'm going to start exercising 3) What purpose does 就 serve here, and does the 就 necessitate the 了 at the end? “就” 也是用来强调，完全可以拿掉： 我从我还是小孩的时候开始画画了 没有 “就” 也得加后面的 “了” 举例： A: 你开始了没？ B: 我开始了 或者 A: 你开始了没？ B: 我很早就开始了！ 在这两个案例中，虽然意思差不多，但B的语气就完全不一样。