If u are an adult who is above 18 yrs old, u are considered a mature student and if u have work experience that counts more as a mature student. In canadian unis, there is this thing as Adult student status to encourage those above 18 to upgrade continually, especially in skills trade or in the Universities.
So if u want to enrol in the Uni or any program such a a Dip in something, then u need to fulfill the basic requirements of that specific program, example, if u want to enrol in a business program then u need high school requirements of some Science 30 or Math 30, but if u cant or have not fulfill such requirements or have not taken such courses at high school, then u can fulfill such requirements at the community colleges near yr place or area or u can take GED, which are exams for u to take, which are equivalents of the grade 12, Science 30, math 30, physics 30, chemistry 30 or any courses, which is equal to the grade 12 standards for fulfillment of the basic requirement in specific programs or majors in unis or colleges.
There are no mature student test except the GEDs or the course specific exams that u can take after self study or attending classes at your local community colleges or after taking the exams. After u qualify for the basic requirements to the program that u want to enter then all u need is to apply as a mature student and the unis will assess if u qualify for the programs.
Hope that helps.