Workers should be paid in proportion to their skills, not their age.
Literal
Workers [to-には], that age [to-に] not, that held skills [to-に] proportional-to, salary [subject-が] paid should.
~に比例して ('in proportion to') is a formal expression. ~にではなく ('not to X, but') contrasts age with skill. A policy argument with nested comparisons and formal passive voice.