initially looking at the photo, i would have to have said that judging from your youngsters height when compared to your height he looks a lot bigger than 14hh!
but then i read you were 5ft1, and then it looked a lot more reasonable! xD
my baby is 12 months and 14.1hh, we've got him predicted between 15.3-16.1hh if thats anything to go by? :)
ive read that you should roughly put two hands on the yearling height, growing anything between 6-10 inches :) you could try the string tests? from the coranet band to the dip in the front of their knee. if it measures, eg, 15 1/4 inches, rough height = 15.1
or the other test, to measure from under the crook of their front leg - all intents and purposes, their armpits - to the back of the fetlock, then this distance should roughly equal the distance above the top of their front leg they will mature to :)
hope this helps!