Q1: When we describe a figure or number between 20 and 30, we can say twenty odd or twenty something. Are there any other expressions with similar meanings?
"Twenty-odd" and "twenty-something" mean different things.
"Twenty-odd" means "twenty, more or less", "twenty or so", "twenty-ish". I would take this to mean "probably more than seventeen, and almost certainly less than twenty-five". Depending on context, I would be most likely to understand "twenty-odd" to refer to a count noun, "twenty-ish" to be the most likely to quantify a mass noun (although it could also refer to a countable), and the others somewhere in between. All of these are informal expressions (especially "twenty-ish"), and the only one that I would ever consider using in formal writing is "twenty or so". I would prefer "about twenty" if I couldn't be more precise.
"Twenty-something" is much more specific. It refers to the nine integers between twenty and thirty, non-inclusive (which is the same as saying "the nine integers from twenty-one to twenty-nine, inclusive"). The adjectival form "twenty-some" is a bit more versatile; I find it can apply to mass nouns, so long as the quantity is greater than twenty, and ideally quite a bit short of thirty. Someone who has just had his twentieth birthday, however, can be said to be "in his twenties".
Q2: Do we need to add a hyphen ie twenty-odd, twenty-something? I guess the use of a hyphen is optional. Is it true?
Again, these are informal expressions that I don't recommend using in formal writing. That being said, I prefer the hyphen in "twenty-odd", "twenty-some", and "twenty-something". These seem to want to follow the pattern of "twenty-one" etc. The words "odd" and "some" substitute for the single-digit number, and therefore take the same form. This is not the case with "twenty or so".
Q3: Is the above use confined to any particular use only? For example, in the use of an approximate age of a person, is it restricted to twenty something or, in other words, can “xxx something”, in fact, be used in any circumstances and is the use not confined to the reference to a person’s age?
If I understand your question correctly, these phrases work equally well with "thirty", "forty", ... , "ninety" substituting for "twenty". My mother died when she was sixty-something, but her mother lived to be ninety-odd years old. Once we get into three digits, though, these phrases don't seem to work as well.
Poor Methuselah. He was only nine hundred and sixty-some years old, and he had so much to live for, but then he got caught up in that flood.
Q4: The more difficult one is to express a figure or number between 10 and 20 as well as 0 to 10. To express a figure or number between 10 and 20, we can say a dozen or so, ten odd. Can we also say ten something? Are there any other expressions? To express a figure between 0 and 10, do we just say “ a few, a couple xxx”? Are there any other expressions?
10 - 20: I'd say there are about sixteen ducks on that pond, give or take a few. Possibly twenty.
0 - 10: There are seven ducks on that pond.
If you can't count to ten, you're on the wrong forum.
Q5: when we refer to a person’s age between 13 and 19, we can say that he is a teen or a teenager.
This is true. In English, the numbers thirteen (derived from the Middle English for "three-ten") through nineteen ("nine-ten") all end in the suffix "teen", hence the word "teenager", which probably doesn't translate exactly into any other language.
what are the expressions of a person aged between 10 and 12?
Is there a reason to have an expression for people of that specific age group? What are they called in your language? Sometimes we call them "pre-teens", but that's rather vague. Babies are pre-teen. Baby girls are also pre-menopausal.
Toddler is a person aged between 1 and 2.5. What are the expressions of a person aged between 2.5 and 10 eg a kid, a child?
"To toddle" means to walk unsteadily, like a drunk man. The figures of 1 and 2.5 years of age cited by your source are generalities. I've known babies that could walk perfectly well before they were half a year old.
This is just off the top of my head, but I would say that someone is a "baby" from the time of birth until he or she is able to have somewhat intelligible conversation with adults. The age can vary greatly among individuals. There is also quite of overlap with terms like "child". All babies are children. When does one cease to be a child? There are different point of view on the subject. A recent thread on this forum cited links to people than insisted that fourteen-year-old "children" can't be held accountable for their actions. I've also known men that served as combat soldiers at the age of twelve.
Q6: To express a figure or number between 101 to 999 and 1001 to 9999, do we say a few/couple hundred , a few/couple thousand, in the hundreds of xxx , in the thousands of xxx? Are there any other expressions? We will say two hundred odd or two hundred something when we express a figure or number between 201 and 299. Are there any other expressions?
Yes, we can say "a few hundred", we can say "a few thousand". We can also say such things as "his salary is in six digits". We can say "two hundred and some". We can say "hundreds of thousands of people died when the bombs were dropped on Hiroshima and Nagasaki". We can say "millions of people have seen her naked since her boyfriend uploaded her selfie after he promised he wouldn't".
Q7: what is the expression of a figure or number between 31 to 99? Tens/dozens/scores?
What's the number? If it's 49, call it 49. Some things (eggs, for example) are commonly sold in quantities of twelve ("a dozen"). A "score" (20) is borderline archaic. Most people in my country are familiar with it only because of President Lincoln's Gettysburg Address in 1863.
I hope that's enough information, because that's all you're getting tonight.