You're right that the timeline is weird. But Donna and her cohort were hippies probably in the mid to late '60s, when they were in their 20s; the movie is set in the mid to late '80s, when the daughter is about 20 and Donna and her pals are in their 40s (although Streep is 59, Baransky is 56, Walters is 58, Skarsgård is 57, Brosnan is 55, and Firth is the only one remotely near the appropriate age, at 48).

But I think the dialog says somewhere that Donna got pregnant at 20, doesn't it? Which hardly allows for the singing career she had before having her baby. Or am I misremembering? And Steep is gorgeous, but she doesn't look 40.

No, the timeline doesn't hold up. I liked it anyway--I adore ABBA.