I used that calculator for fun on my "kids" who are now grown and mostly grown. It was several inches high at age 2 for all three of them. My older son who is now 25 was predicted to be 5'8" from age 4 on, and that is just about exact. My younger son is 16, so he may still grow. For the ages that I did between 4 and 10, it said 5'9" (about where he is). Based on his 15-year old height, though, it's saying 5'11"...we'll see. My 22-year old daughter's jumped around by a few inches but it pretty much landed her in the right vicinity.
Didn't realize that I got caught in an old one! And I don't see how to delete my post...