What To Do When Too Many Old People?

New York Post
Japan reaches new world record
with 1 in 3 people over 65"New government figures show that the country now has the highest ratio in the world at 35.6 million senior citizens, which is about 28 percent of the population. It’s followed by Italy at 23 percent and Portugal and Germany, both with 22 percent..."

In 2016 the United States had 15.2%. In 2040 it's estimated there will be 21.7%. By 2060 an estimated 24%. I've always thought it a good thing when there isn't a boom in population. However what do you do when there aren't enough younger workers to replace them?

Perhaps the solution could be by allowing greater immigration of younger workers. Hopefully because of increasing automation they won't be necessary. This leaves us with the question whether society can continue living at the current level if less then half of the population is productive without importing younger workers?

I mentioned less then half keeping in mind about 10% are sill in school. Another 19% are disabled here in the United States.