Unfortunately, it's normal and I'd say it's really really random and luck based, no matter the sublevel of certain skill (i.e. 13.1 or 13.9 dropping to 11) and the trainer level and his specialty. I have the same trainer as last season, and I had a 34 yo player who had 1 skill drop the entire season. This season on the other hand, I have had 2 double drops for one player, and 2 more for 2 separate players, alongside a decent amount of usual 1 skill drops. Just the way it goes with players once they hit 33 and older