Sure I would agree. Not many of us saw our great grandparents but I'm sure they are also like what Shakespeare described in his poem. The last stage is more like the oldest stage of life where the old now depends on other people. They become useless and are always forgetting even the simplest things. Where they would lose their teeth, vision, taste and everything they worked hard for their past stages.
we will soon experience this stage, that is, if we don't die early.. :)