Temperature, like age, is one of many factors that determines when a spirit is ready, but it's a mistake to think that because rums are aged less that it's because of the climate. The congeners are also significantly different, just like those between bourbon and scotch, and the processes all vary in order to get the specific flavor profile the distiller wants.

Yes, there are 3 year rums that taste like 18 year scotch. And there are 18 year rums that taste like 8 year whisky.