This is clearly in the fuzzy definition area since your argument is that you have gained enough experience in this area to give subjective life advice, the argument against simply has to involve a judgment of your level of experience.

In the same way that I can't meaningfully ask "am I attractive enough to professionally model?" and respond to every "No" with "ad hominem!", when you bring your person into the argument as support, either implicitly or explicitly, the scope of things classed as ad hominem fallacy is constrained. Ad Hominem's are also in the class of fallacies that can still inform a decision even if, like all logical fallacies, they cannot prove anything.

To exit the pedantic logic argument for a second: That confidence and directness is a good practice, and writing practice and avoiding seeming unsure are great reasons to do it. In my experience if you also use that confidence and directness to preemptively address potential weaknesses in your argument (as in "I know I'm new at this but here is exactly why, in this case, I am right anyway") you are even more convincing.