@ican711nm,
It is discrimination if a standard is set that would be impossible for you to meet such as a minimum height of 5'6" and you're 5'0", or you have to be able to withstand a tackle by a 300-lb line guard and you weight 90 lbs. So far as I know there are no such restrictions for gaining an engineering license, however. Anybody of any height, weight, race, sex, sexual orientation, ethnicity, or age can qualify if they are able to master the disciplines and go through the necessary process. Yes, one's circumstances can make that much easier for one person to accomplish than another, but one's circumstances are not dictated by the rules governing licenses nor do the rules take into consideration one's circumstances. Nor should they.
And so it is with a marriage license. Anybody and everybody can qualify but everybody has to follow the same rules. Such rules might make make it difficult or impossible to marry the person you might want to marry, but the rules don't address who you want to marry but rather only address the process by which marriage will be allowed under the law.
Neither is discriminatory.