By the time your child reaches this stage, he is definitely in a position to understand a lot of things around him, if not all. But, the question is how much he understands and what he understands. Any understanding that is partial and insufficient can be damaging beyond imagination.
What you need to do
Let’s talk about death, for example. At this age your child might have seen someone passing away in the family. The member could be someone close or a far off friend or a relative. But, in either case, the child is bound to come up with questions, which are difficult to answer. The concept of death itself could be extremely uncomfortable to talk about if you yourself are grieving. Perhaps, something that would need extreme precision as the slightest misjudgment on your part can hamper the psychological development of the child immensely. Remove the word 'death' and substitute it with 'passed away' or 'gone to sleep'.
Don't over load him with the stark philosophies of life, rather stick to the queries that come from the child’s mind. Excess information might confuse him further and that can do more harm than good. Be truthful in all possible ways - “I have sad news, your uncle Joe passed away today”. Do not hide your emotions. Show your sadness and grief. Explain your feelings elaborately and not vaguely- “I am crying because your grandma passed away and I am not going to see her again. I loved her so much. Will miss her.”
Your child will learn this is normal, and he too can do so. Understanding such quintessential elements of life can be tricky, and presenting them to your kids is even more difficult. So handle it with care, and you may find a path that does good to you and your child, in every sense.