30 years here, and the mania is well controlled, but the depression hasn't gone away in 9 years. (I have a reaction to all of the SSRIs, and unfortunately, serotonin is exactly what I need to stabilize my depression.)
Winters are the worst for me, with a slight hypomania as spring arrives. (And I love every minute of spring!)

It does seem that the depression gets worse as I get older, but I can't verify that, as I go thru shrinks about as fast as most people go thru a box of cookies. (They keep moving, quitting or retiring on me..)