If youre young and have a strong immune system, will foodborne illnesses still affect you?

Very much so... Food borne illnesses encompass anything that can make a person i'll, that is found in the food that was consumed. This includes not only bacteria and viruses, but also toxins produced by germs. In situations such as food poisoning resulting in vomiting hours after eating, it may be due to a toxin ( eg staph food poisoning)- in which case a "strong immune system" isn't that useful.