I read the Harry Potter books as they came out. For the first four, I was younger than the titular protagonist and really connected with the books as a result. By the time Harry Potter and the Deathly Hallows came out, I was a couple years older than Harry (because J.K. Rowling took a few years off between the later installments) and definitely was missing the connection but still mostly absorbed by the drama and incredible fictional landscape. The writing of the last few books was at a higher level, too.
Had I picked the books up as a 17-year-old like @
Fig, though, the first two would have frustrated the hell out of me, and I never would have reached the more complex and well-written stages of the series.