None of these are particularly strange…
RMS Titanic - I went through a phase when I was 7 or 8 years old that I was absolutely obssessed with the ship and its 1912 loss. My mom tells a story about me once running home so excitedly from school and bursting through the door, she thought I must have gotten an A+ on an exam or gotten my first kiss. I shouted, “Did you know that the bars on British ships open at 2pm on Sundays?” (or some other similarly obscure factoid; I don’t remember the incident but don’t doubt her in the least).
World War II, especially warplanes - In my early teens.
Star Trek and Star Wars- In my later teens, and still a bit today.
The American Civil War - From the time of the Ken Burns PBS series, more or less through to today.
LOTR and Tolkien’s other writings - For a couple of decades now. When my older sister, whose interest in Tolkien long predated mine, said (unprompted by me) that my knowledge of Middle-earth had surpassed hers, I was one happy camper.
American historic flags - Since my Boy Scout days.