Here's the marriage certificate of Anne THOMSON and Henry deKoven RIDER:
https://a860-historicalvitalrecords.nyc.gov/view/7891912
It says Anne would turn 20 on 11 Apr 1888. And Henry would turn 25 on 21 Jun 1888. Sometimes the birth years can be off, however.
Curiously, I recognized the name and signature of one of the witnesses: Edward Kindberg, who was a specialist in prints and engravings and was an employee of the antiquarian bookseller William Evarts Benjamin in the 1890s.
Yes, I have the marriage details of Ann and Henry De Keven Rider and Edward Kindberg who married Ann's sister Isabella Thomson in 1885. She died quite a gruesome death in 1908 and there was a lot of newspaper articles about his will after he died in 1909. That's why i mentioned in my first post that i knew a lot about the rest of the family and was looking for William, Isabella and William Jnr.