Is anything alive? If so, define life.
Life is a concept used for labeling differentiated classes of objects. What constitutes life is conceptually indeterminant and somewhat arbitrary. Like any term or concept it can be altered by context, so the important information will be the relevant contextual information in the discussion. For instance, "life" in a discussion on biology will likely signify something different than in a discussion about AI or abortion. As long as parties to the conversation are on roughly the same page, minor discrepancies in usage should not be a significant issue.
All living things consist of the same basic components: the ability to grow and adapt, the ability to develop physically, being made up of living cells, requiring some outside substance to sustain life force, etc. There are many things that are scientifically "living" but if you are referring to sentient life then only humans are truly alive.
Chimpanzees are close enough on the evolutionary tree that they exist in a gray area of sentience. The clinically retarded (depending on exactly what is wrong with them) have little to no experience of the world around them. At least not to the full extent compared to someone who is not clinically retarded. The clinically retarded can still experience the world but will not feel the same kind of emotions as someone who is mentally normal. Therefore someone who is clinically retarded (once again depending on their condition) is not as sentient as someone who is not.