Facts:
1) People live longer, much longer. In the 1950s, a person would have an expected life of just a few years after retiring. Now it can be 20+ years.
2) There are less babies being born, for quite some time now. As a result, the proportion of people that are active in the labor market is shrinking.
3) The pension system in France pays people above and beyond what they contributed over their working years. The gap is closed by contributions from those still working.
4) By keeping a retirement age which is completely out of whack with demographics and progress in medicine, France is saddling its younger generations with a heavy tax burden.
5) Money does not grow on trees.
6) Taking money from young people, and giving it to old people, reduces the amount they can spend on a new house, or a new car. You know, the things that power an economy.
7) Old farts don't buy houses, and are often content with driving old cars.
8) Macron is trying to make the French economy more dynamic.
9) Forcing people to work another 4-5 years, produces that much more tax revenue. Not having to pay them pensions at the same time, means less expenditure. Result - more money to invest in things that will make life in France better over the long term.