There sure is a lot of talk in the play about old men being like "babes again" (1.3.3), isn't there? Check out this passage, where Lear announces his decision to transfer the burdens of kingship to the younger generation:
[…] and 'tis our fast intent
To shake all cares and business from our age;
Conferring them on younger strengths, while we
Unburthen'd crawl toward death. (1.1.2)
Wanting to retire and "shake all cares and business from our age" is understandable – it seems that King Lear is ready to kick back and enjoy his golden years. [By the way, it's pretty common for monarchs to go around referring to themselves in the plural (we, our, etc.) instead of the singular (me, my, etc.). This is called the "royal we."]
What's curious about this passage, however, is the way Lear conjures up an image of a feeble old man who, unable to walk upright, "crawl[s]" around on the ground…like a baby. What's up with that? The image suggest that growing old is a lot like being an infant again, which means there are no responsibilities (what Lear wants). Unfortunately, it also means that old age leaves one weak and powerless (not what Lear wants). Lear's not the only one who sees old age in this light – his daughters, Goneril and Regan, are more than happy to treat Lear like a baby and Lear finds that the powerlessness that comes with growing old can be pretty painful and humiliating, especially when his own daughters go around saying things like "O, sir, you are old […] you should be ruled and led / By some discretion, that discerns your state / Better than you yourself" (2.4.4).
Shakespeare's point? Getting old sucks.