Yeah the math is a LOT more complicated than that. You just say say "only 25% of employees are 41+ therefore this was discriminatory" unless the goal of the layoffs is a normal distribution of ages company-wide, which I think is unlikely.

What departments were affects most? Was seniority a factor? Was pay a factor? Were certain projects, departments, or teams exempt from layoffs? Without having very detailed data about who was let go and what the justification was nobody can say whether it was discriminatory.