Sorry, but it is not just LinkedIn, society as a whole became ageist.
One example is retirement: you are supposed to work and save enough money until something from 60 to 70 years old, depending on your country, but if you lose your job after 40 (and you will, not because you are a bad employee, but because they will hire someone younger than you to pay less than pay to you), you won't find another job to earn enough to live and save for retirement.