If you are over the age of 18, and have not yet finished your grade school education, you may find you need a high school diploma (or equivalent) to qualify for post-secondary education, enrol in a training program or get a job.
In Alberta, a student is considered to be "mature" if they have reached the age of 20 by the start (i.e. September 1) of the current school year. Once students become mature, the Alberta Government will no longer fund their education, and those wishing to acquire a high school diploma (or equivalent) must cover the cost of their education.
There are a number of ways for mature students to get the education they need to enter post-secondary, the trades and/or the job market. The best method for each student depends on their individual situation - for example, the number of credits they have already earned, and/or the requirements of the education program or job they wish to enter.