I cannot find any source supporting this claim, and I’ve mostly heard they ripen in ~7-8 months in northern CA, though I don’t have personal experience ripening them myself in non-ideal climates yet.
For example, when I’ve bought Mexicola fruit and seeds from @Marta, they were typically ripe in September/October, after flowering in late winter (same year). She was growing them near Davis, CA, not the tropics.
Most avocado guides for the SF bay area suggest Mexicola because it will ripen before winter. E.g., here’s a blogger in the SF bay area:
Traditionally, a Mexicola tree is harvested September through November, although we find our trees produce well into November and even December.
Greg Alder lists Mexicola as the very first cultivar to ripen starting in September in southern CA:
Julie Frink lists Mexicola as ripening in November in Irvine:
https://www.ocfruit.com/files/Avocados.htm
Epicenter Avocados, in northern CA, says this about growing avocados in the SF bay area (emphasis mine):
With a Mexicola or Zutano, the temperature required to kill buds is several degrees lower, and the delay until the next crop is reduced because they ripen 7-10 months after bloom instead of 14-18 months for a Reed or Hass.