Which age-gates should be skill-gates and vice-versa?

In the UK, it is illegal to buy alcohol if you are under 18. Similarly, in most countries, you cannot vote until you have reached a specific age. These are age-gates. You do not need to prove your competence to drink, vote, smoke, or get married; you just need to be old enough. Some things have skill-gates. If you want an amateur radio licence in the UK, you need to pass an exam. You can be any age0. Similarly, most jurisdictions allow you to get a medical licence once you have passed the requisite tests1. There are also activities which are dual-gated. You can only get a driving licence after passing a test, but you can only apply to take the test once you are a certain age. Where should society swap age-gates and skill-gates? Perhaps the big one is voting. The UK is preparing to extend the franchise to all 16 and 17 year olds - but why is there an age-gate at all? Children are affected by politics, they pay tax on the goods they buy, they exist in the world. Why shouldn't they vote?…