Well, I personnally would wait till he is at least 9 months to a year before giving him a wheel. He is still a growing baby and needs all his nutriets to go towards a good growth.
When you do put the wheel in, be patient. Sometimes it takes them a while to figure it out and sometimes they just don't care fore it. Time will tell, actually a customer of mine's girl took over 3 months for her to get on it and now is enjoying it fully.