When did the penitentes form?

Answer 1

If you mean when did they form then the answer is all the time!!

If you mean how did they form, then (I did write this myself):

Made of compressed snow and ice, these pinnacles only form above 4000m, through the process of sublimation. Sublimation is when a substance goes from the solid phase to the gas phase without passing through the liquid phase. This happens due to the dry air in high altitudes. Some areas sublimate faster than others are, resulting in random depressions in the surface of the snow. Sunlight is focused on these curved areas, causing them to sublimate even faster, forming the tall spikes (penitents).

Answer 2

Penitentes form at high altitudes in snowy regions where the sun's rays are strong and the temperature remains cold. They are usually found in regions with high solar radiation, typically above 13,000 feet (4,000 meters) and are most commonly seen in the Andes mountains in South America.