That's what I thought too; he was baptized at age 19 and left at age 21. I asked why did you stay in it for so long then suddenly decide to leave? He said it seemed to make sense the way it was explained why all other religions are "wrong", but finally left because they had no better arguments for why JW is always "right".
But, like yourself, I don't understand how a thinking person could join a relatively marginal religion like that. Not only does it forbid the celebration of anything except weddings and wedding anniversaries, but it doesn't allow members to pursue higher education or vote.