My daughter has always taken her time chewing her food, especially meats, and when she was younger (1-1/2 to 2) she would get down from the table with food in her mouth and eventually get tired of trying to chew it or don't like the taste/texture anymore and just spit it out. We got SO tired of picking up sticky, wet, half-chewed food, or accidently stepping on it w/o shoes! EW!!!! I started making her clean it up. She hated the feeling of it in her hands just as much as we did and stopped very quickly. I had to guide her hand since she was still too little to understand just me telling her to pick it up. If she doesn't want something she can spit into a napkin or into the garbage can. Also we instituted a rule that says the kids (there are 2 - 9yo boy and almost 6yo girl) must ask permission to be dismissed from the table after they are done eating. If they get up before they're done, their plates get cleared (we are still fighting her on this one...she is stubborn).
Oh, and with older siblings it is common for kids to take their time speaking. Why talk when big bro/sis does it for you?....If he is saying words, just not speaking, I wouldn't worry. If he hasn't even said one word then maybe consider having him evaluated.