Yaarel
🇮🇱 🇺🇦 He-Mage
At least for Nordic-esque cultures, kids grow up from around the age of 8 learning how to fight, including Athletics wrestling. Adolescents are very likely to know how to handle a shield without being familiar with light armor.yeah, one solution could be to link it to light armor.
Yes. That is why a choice between shield training or proficiency with one martial weapon, or one cantrip, is appropriate at level 0.a shield is as difficult to use properly as is a sword, so no I wouldn't give it to everyone, especially bookish wizards who need to focus their hands and learning on spells. Besides they already get the Shield spell.
Keep in mind a shortsword is a simple weapon, and many kids are likely learn a shield and shortsword.