Do you offer breast before solids? This is the way to ensure that he will still get his milk. Up to one year, milk is supposed to be a main source of nourishment for infants, solids are just for fun and to introduce little ones to the different textures, tastes and so on. If you offer breast first and he still takes as much as he does, I would say he knows what he is doing. Babies actually become efficient eaters around 8 weeks and some may be done in even 5-10 minutes so your little one is not unusual.
However, if you offer solids first and tend to overload him, he may not be hungry for milk. In this case you need to change the sequence and start with nursing, then 45 minutes later or an hour later (or whatever works for you and him) offer solids.