Life as an organic replicator seems as good a shorthand one as any, though even if a particular organism is incapable of replicating (some defect in its biology) that wouldn't make it not alive, would it?
Here as well are the doorways of age 20 and 40 and 70 and (should we live so long) of ninety and beyond. Here at the end, is the final doorway – or, at least, the final doorway that we are able to see.