Recommendations are just that...recommendations. You will know if he's ready...does he hold his head up well, seem hungry, yell or grab for other people's food at the table, etc? If you try giving him a bite and he pushed it all back out (give him a few chances) then physically he isn't ready.
And so many people will tell you "oh, food is only for practice, not nutrition" for the first year, but I just don't believe that. That's what I did with my first one, and she's a terrible eater. Picky, and eats like a bird, but loves her milk (still) at age six.
However, I started with number two around 4 months, and by 6 months we were well onto fruits, veggies, and little finger foods...and she eats wonderfully. Also, she isn't overweight...however, my first, who got all her "nutrition" from milk, was.
You'll know...just follow your instincts!