Boys are funny, puberty hits at such a wide gap. The rule tends to be that the later it hits the taller they will be so you may find that's about it - or maybe not 
I've recorded it all in the red books (yes, i am that person!)
DS1 was 167.5 cms (about 5'6)and DS2 was 174.5cms (5'8.5) - both measured on their birthday. DS1 was taller than DS2 up until early teens (Ds2 hit puberty at a younger age) DS1 is the tallest.