Hey Davina! (Love the name, by the way!)
I'm not completely sure I'm understanding your first question right so feel free to correct me if I'm wrong.
Using the levels you've provided, with Divination being a six, that chart shows what type of "divining" your character would be capable of. At level six, your character's "danger sense" would allow them to use their sense of smell to detect when something might not be quite right. A level six in Divination also allows the character to see medium colors in a subject's aura. For predicting the future, a level six allows the character to detect if a general area of the future is good or bad. And a level six would allow the character to know exactly where a spirit is, but they cannot see it. A level six would also give a character the abilities of levels one to five.
Basically, you find your Divination level on that chart and then match the letters along that row to descriptions below that chart to know what your character would be capable of.
Again, if that's completely off base, let me know. I'll try to catch you on private chat to discuss it more.
There isn't really a minimum "adult" level because you don't have to take all 32 levels if, perhaps, your character is not particularly good at magic. The main idea is just to keep the levels balanced so that the lowest level is not less than half the highest. Think of 32 levels as what the "average" person would have earned during their years in school.
The time warp did happen right at the start of 1975 and the wizarding world did go back to 1937, however, the current IC year is around June of 1945 so it has been around 8 years since the warp.
Yes, there are 3 IC years to every OOC year. The first three months (January-March, May-July, September-November OOC) would basically be like September-June in real life. The fourth month (April, August, December OOC) is the summer months. Like July and August in real life.
And, yep, you've got that last question right in your second post. The entire magical world (and everything within its borders) "slid" back 38 years. No one will find their younger selves walking around or encounter other relatives suddenly living in their house because those people were on the same backward slide.
Let me know if this answers everything! If you'd like you could send me a personal message to discuss anything as well.
Welcome to the site!