I don’t want to worry you, but you might want to consult a specialist to rule out autism. Aggressive behavior and delayed speech patterns are common symptoms of autism. Also, consider enrolling your son in a speech therapy program. The sooner you get him started on speech therapy, the better will be the outcome.
Check this: http://www.khovnanianchildrenshospital.com/KHCH/services/pediatric_rehabilitation/Our-Speech-Therapy-Program.cfm
If you are concerned about autism, you need to see indeed a speech therapist and a psychologist.
You should not judge your own or others feelings what is this - check with a good specialist.
If it is an autism: the earlier you start the treatment - the better it is. If it is not (speech delays could be due to multy-lingual environment or even high IQ) - great, that's easy to treat.
My son has an autism and I really do not appreciate a pediatrician who were telling us for 2 years our son has a speech delay because of multy-lingual environment. We lost so much time because of that!!! Just find a good child psycholog, who saw autistic kids before and not just a regualr school/kindergarten psychologist. Even child psychyatrician would work.
My son has a speech and language disorder, and has the understanding of a 2.5 year old. I suggest you take your son to the doctors, or go and see a speech therapist. Maybe he's just a slow learner. He will need help so see a speech therapist.
The speech delay usually shouldn't be a huge problem. Some children start speaking later than others. Keep practicing with him and giving positive feedback to encourage him. As with the hitting, you are the parent and need to put him on time out and make sure he knows hitting is not ok. He is acting out and if he knows he can get away with it, he will keep doing it and it can get much worse, so stop it now while he's young.