I was 29 when I got the J Pouch and I am now 57, so I have lived almost half of my life with a J Pouch. Next April it will officially be half of my life as both my J Pouch Step 1 surgery Anniversary and my birthday are in April. I believe I was technically still 28 when they did step 1, and turned 29 just 12 days later.
But if you consider step 2 the deciding date, then it will be later in 2021 when I reach the theoretical "half of my lifetime with J Pouch" mark.