An input field takes the year of birth between 1900 and 2004.

Boundary value analysis focuses on the values at the edges of equivalence partitions. For an input range of 1900 to 2004, the boundary values are just inside and just outside the range:

Just inside: 1900, 2004

Just outside: 1899, 2005

Therefore, the boundary values are 1899, 1900, 2004, and 2005. Reference: ISTQB CTFL Syllabus V4.0, Section 4.2.1​​.