I first read a treehouse book when I was 8 (the 39 storey treehouse). I am now 17 and I have just finished the last treehouse book (the 169 storey treehouse). I have read the whole series (including some many many times) and they were a big part of my childhood. I loved them so much I even tried to make my own version with my friend when I was about 10 (we only got as far as making a cover). Thank you for fueling my imagination.