He's not too young to CIO. We did it perhaps a little early, but when she was five and a half months old she was still waking every two hours at night to nurse, and I needed her to go three hours so I could be a sane mommy during the day. So we used it then with great success.
If you decide that's what you want to do, be sure you're committed to it and that your hubby (if he'll be around when you're doing it) is also committed. We used CIO and there were a few times when we stopped each other from going to our LO when she was in the middle of a crying fit. It's rough when you're in the middle of it, but I subscribed to Dr. Weissbluth's ("Healthy Sleep Habits, Happy Child") theory that the total amount of crying is less if you use CIO vs. a check and console (like Ferber's method) and it certainly worked for us. My LO (12 months old now) goes to sleep extremely well in her crib for naps and bedtime.
You just have to make your own decision. If you're not able to stick to letting him cry then you're co-sleeping, so accept it and be happy with it and enjoy the snuggling. We used a co-sleeper next to our bed for her first five and a half months, but she only slept in the bed with us a few times and only slept on us when she was very little. Sometimes I wish I could snuggle in bed with her, but I'm glad that my hubby and I have our bed for ourselves and I know I get better sleep without her in our room!
The book that someone else referred to is (I think) by Elizabeth Pantley, called "The No-Cry Sleep Solution." I read it also - if you decide to continue co-sleeping I'd recommend reading it.
If you go for CIO, read Dr. Weissbluth's book.
Good luck to you! Either option is completely valid and neither will cause long term harm to your child. Just pick whichever works best for your family and be comfortable with your decision.