Where is Gladys in the 1901 census, NW or SW England? What age and place of birth?
I think both need their ages checking in 1911 and 1921 to form likely conclusions.
I have corrected Gladys' birth from Salford to Northleach in reply #5, but that means she was 33 at the marriage in April 1925, not 22 as on the cert, because she would have turned 33 on 3 Sep 1924 (and was probably registered in SepQ).
If William George Mallett was born 2 Apr 1892 as per 1939 register, then his birth must be the registration in Gloucester, JunQ 1892 and he was 33 at the marriage.
If he was born 2 Apr 1894 and registered at Crediton, he had just turned 31 before the marriage on 25 Apr 1925, but his birth must have been registered at least 3 months later, in the Sep quarter.
I think! Please check my calculations.