Different contries laws are wery various. Some condtries dont have hard age limits, but another ones have. The most popular reason why companies reject job applicats is the age. In my opinion, this is good leads to the development of companies, but it causes people to be unemployed.
To begin with, when some contries, the main reason why it is illegal for companies to decline job applicants based on age it creates fairness about job opurtunities for every age group. The quality of work depends on skills, not age. For instance a job can be done better by a fresher, who do not have any experience, but hard- worker, faster and more skilled person than by an older person with more practice. So the old people can use their experience to improve that business.That is the reason why denying job candidates for their age is illegal.
In addition, if it is not illegal companies can take only old people and younger people be unemployed. It cause the increase in unemployment leads to a decrease in welfare and poverty in that country. This can make government more pressure and it is so difficult to improve the economy.
In summary, I think hiring younger and more skilled, hard- worker personnel will make companies work better. Then it allows for equal opportunities and encourages a balanced workforce between experiences and knowledge.