This is Townsend's personally felt lament to the way a decline in a couple's sex life so often leads to the overall decline and disintegration of the relationship. He tells of it primarily from the point of view of the man, whose libido and performance both tend to diminish with age.
Andy from FloridaEric from Virginia; I have to disagree. I think you have the first part right about the disintegration of the marriage - there are plenty of lines to support that - but with regard to her attitude, it talks about how they both have become stagnant - "we have to be so drunk to try a new dance" "she wouldn't dare in those slit skirts" - that suggests he's upset that she has to be drunk just to do anything new...
Eric from VirginiaOh God no. No, No, NO. A thousand nos! (to B.D.'s explanation)
There are a couple of lines in the second verse that can be read as referring to sexual performance, but that is totally missing the point of the song.
This is an incredible meditation on the disintegration of a marriage in middle age. A meditation bristling with frustration, anger, defiance, disappointment -- you name it.
Townshend is both ruing the loss of his youth and the opportunity, romance and idealization that accompanies youth while also saying that his ex (Jeanie) will never be some middle aged faceless woman in a slit skirt desperately trying to find someone new. And he won't be some middle aged wanker in a ripped shirt doing the same. He's ruing the loss of his marriage and of his youth while simultaneously giving the middle finger to being some desperate middle aged has-been. And that his ex is too good for that also.
An absolutely brilliant -- and defiant -- meditation on aging, loss, and heartache.