*compared to when I was a child

I read a book written by J.R.R. Tolkien. (He did not recently die. It is common knowledge that he is dead) I have more hobbies than I did as a child. (Yikes!)

The B sentences are stylistically poor. When you compare two things, try to make it clear exactly what the two things are that are being compared. Neither sentence does this well. If you really want to compare "I" with "(the) child me" (as your sentences do) then you should make that comparison explicit: "Compared with my childhood self, I have a bunch of hobbies." Since the two things being compared are placed right next together, the comparison becomes obvious. But, really, that comparison is not a very good idea. You are comparing yourself with your childhood self. You can do that - in fact, it's rather poetic, but it is nonstandard. It would be more sensible to compare your current hobbies with your childhood hobbies: My current hobbies are copious compared to those I had as a child.

A2 is correct. Regarding the second set: neither is correct.

Group A: - A1. "I read a book written by late J.R.R. Tolkien." This sentence sounds unnatural because we typically use "the" before "late" when referring to someone who has passed away. - A2. "I read a book written by the late J.R.R. Tolkien." This is the natural and correct option. Adding "the" before "late" is standard in English to indicate the person is deceased, and it makes the sentence sound complete. --Preferred: A2-- Group B: - B1. "I have a bunch of hobbies compared to child me." This is grammatically understandable but sounds awkward. Native speakers don’t commonly say "child me" without "the." - B2. "I have a bunch of hobbies compared to the child me." This sounds more natural. Adding "the" makes "child me" a specific reference to yourself as a child. It follows the pattern of referring to "the past me" or "the younger me." --Preferred: B2-- Why? In both cases, "the" is used to clarify the noun: - In Group A, "the late" is a set phrase used to refer to someone who has passed away. - In Group B, "the child me" works as a specific reference to yourself in the past, making it sound natural and complete.