How much should one limit their training load increase for year to year? this is assuming they have unlimited time.

Here is a example is a person is only training about 13hrs per week their first year of training how much would one be able to increase their training load?

It depends on what you're training for and the makeup of your training. It would be no problem doubling your previous years training if you didn't have much intensity. On the other hand 600+ hrs/yr is plenty of training for a Cat 3 racer.