I don’t know that it was supposed to be a concept album about that, I think that’s just where Pete’s head was at. From Wikipedia:

The songs on the album were, for the most part, more introspective and personal than many other songs that the band had released. Townshend’s 30th birthday occurred in May 1975; he was troubled with thoughts of being too old to play rock and roll and that the band was losing its relevance.[4] He began to feel disenchanted with the music industry, a feeling that he carried into his songs. He said of the songs on the album:

[The songs] were written with me stoned out of my brain in my living room, crying my eyes out… detached from my own work and from the whole project… I felt empty.[4]

That’s sad, but I think the juxtaposition of Pete feeling old with Pete sitting around on the couch getting high is kind of funny.

I relistened to the album today. I think it’s decent. I’d say that it’s aged less that Who Are You, and also kind of shows the band aging more gracefully than they did on Who Are You, but Who Are You has stronger highlights. I do think that By the Numbers is something of a different animal than the other albums from Who’s Next through It’s Hard. It very much sounds like the same band, but they synths that are all over those other albums are nowhere to be found.

Squeeze Box is a weirdly juvenile song to be on that album.