I assume you are not doing breast-feeding, because if you do, protein shouldn't be of any concern. If you are not feeding him safe baby formula, you need to be very careful with what to supplement as protein intake. Babies under 12 months can not digest pretty much any other kind of protein except mothers' milk; because baby's digestion system isn't fully developed.
Tofu is made from beans, beans is much harder to digest than most vegetables because they contain high level of protein, they generate gas during digestion process, it can cause severe stomachache to a baby. You should check with a pediatrician before feeding him tofu. And I remember I was told by my pediatrician in the States not to feed my baby any cow milk or egg or honey or any processed nuts product(like peanut butter) until he is at least one year old.
At 6 month, you can give him thin rice cereal(or mix with oats cereal) and soft fruit and cooked(processed) vegetables; add other protein after he is 12 months old.