Most universities do not specify an age requirement for pursuing a MSc in Mathematics. The basic requirement is thematic academic qualifications, which concerning a degree in mathematics or a similar field. Some universities may have some age preferences for certain programs that seem to target younger fresh graduates. But these preferences are usually non-binding, opts for younger candidates because of the nature of the program.
When there is a notable age gap between the learner and other cohorts, challenges may arise in the academic setting or with career advancement. On the other hand, properly motivated adult learners who meet the required academic standards do not have to worry about confronting age restrictions. Universities value diverse experience, hence mature students are allowed as they give a different outlook. It is better to seek information from each university individually to see if there are age restrictions or special provisions for mature applicants.