Would the applicant age be a barrier when applying for certain jobs although the Job details have no age specifications ?

In Arab world, Yes it will.

For any other country, NO.

In selection and recruiting the most important thing is the eligibility to do the job tasks mentioned in job description, as long as they put clear preservation. 

Age can be a barrier when trying to get a job but it shouldn't be. Most companies state that they don't discriminate against a person's age or gender but they still prefer having young people being employeed compare to older. It also depended on the type of company, the specific field, and the salary.

Depending on the type of an industry ,it can be a barrier .In a customer services industry it is but other it isnt .

Age barrier can depend on the job profiles. Certain job profiles can have age restrictions and I feel its justified. Like being a pilot.

No i dont think so that it should be the case

Yes it can be depending on the demand of the job.