I was hired on april 3rd 2017 as an advertising salesman for a magazine and dismissed April 20th 2017. The reason this isn't working out. Is that legal? I have a suspicion, it is age related.

Employers can terminated employees at any time, without even having to provide a reason, if it is done so on a 'without cause' basis and you are paid your legal termination entitlements. If any of the reason for your termination was directly related to your age than you would have grounds for a human rights claim as well. However, you must be able to show that the employer clearly discriminated against you on the basis of age in employment.