I'm looking to buy a new bike for my 11-year-old son, but am in a dilemma. He currently has a Ridgeback MX20 which is too small for him. He's 4ft 9 (144cm) and I can't decide between a junior MTB with 24inch wheels, versus an adult MTB with 26 or 27.5 inch wheels and an extra small frame. I don't want to buy a junior bike only to see him shoot up in height in a year (all the men in our family are over 6ft so chances are fairly good he'll be tall). I've been comparing the Scott Aspect 670 or 770 (with 27.5 inch wheels) vs the Scott Scale Junior 24. Clearly I don't want to buy a bike so big it's dangerous, but equally, I don't want to see him too big for a junior bike in 6-12 months. Any thoughts?