What year or decade could this picture be from?

1924

The ladies do look very mannequinesque (if that's a word). It isn't the carriage at Covent Garden.

There are anachronisms.

The clothes, and especially the hats, on the dummies are in the "flapper" style, dating from the 1920s. However, the line diagram on the left wall has a caption reading "Metropolitan Line", so it dates from after the formation of LT in 1933. Indeed, as the caption is purple, it dates from after about 1950: before then the Met was the same green as the District.

I suspect the carriage is preserved somewhere with its interior in the state it was in when withdrawn in 1961 following the introduction of the A stock. To add some life, the dummies have been put in the compartment, dressed in clothing appropriate for when the carriage was built.