Personally I care little for most age of consent laws, they're usually not based on anything other than what minimum point made the person writing the laws stop feeling icky or the maximum point a morally protective sort thought they could get away with, neither of which is a good basis for laws, even if it is annoyingly the only method we have to determine some.
Historically they've varied wildly usually depending on how fast children were expected to act like adults, which was frequently as young as 12, younger in some times and places, because of how deadly life could be. The Norse used to marry between 12 and 18 (18 being the extreme outlier) and have kids before 20 because they only got 30 years or so to get their kids to adulthood before they dropped dead of malnutrition, cold, wild animals or getting stabbed by somebody.
Here in the UK it was 12 from 1275 to 1875, then 13 until 1885 when it became 16. It almost became 17 in 1917, but that was beaten by 1 vote.
Ideally I'd like there to be a proper scientific investigation into the way people's brains, personalities and bodies age, done on a properly representative (for the species, which means large sample sizes would be necessary) scale, that served as the basis for consent laws, but I expect the answer would be a fairly useless 'it varies from person to person,' and would take decades in any case, not too mention trying to get funding for such a large project.
Based on personal experience there are people who are perfectly mature enough from a young age, I would in hindsight say I was mentally suitable from about 14 (never actually bothered until much later on,) but I've met plenty of people well into their thirties and beyond who I would not consider of sufficient mental maturity to consent and most of my peers as a teenager would not have been what I would consider mature enough to consent.
]To paraphrase it, the people can't handle the truth. Or better, they're not yet ready for it. The society must be divided in parts, or classes, in order to avoid unqualified people getting access to information that is legitimately dangerous to them and to everyone around them. The only question is how to do it without making it undemocratic and tyrannical.
A good start would be formal training in logic, philosophy and civics as part of education from a young age. It would probably be a better use of time than learning about religions or (non-modern) history.
It would be good, but, sadly, those concepts are a little bit too advanced for everyone to handle. And it's not particularly democratic.
I do have an idea on how to combine both democratic and qualification concepts at the same time. The citizens should be asked to pass tests - questions and answers for which should be made by citizens themselves, to ensure the proper democracy aspect (and yes, this means that there'll be inevitably some portion of "troll" or "insane" question/answer pairs - smart people will still tend to answer them better than the dumb ones, if not in a "truthful" manner) - and then the, say, top 20% in terms of number of answered questions, will pass forward to the next level of qualification. You can iterate that to get higher "citizenship" levels, where questions/answers for each level are made up by people of at least one level below and higher.
This "citizenship level" probably really shouldn't have any formal/legal powers, but it should instead serve as an informal sort-of-democratic-indicator of general expertise and being in touch with the people. It could probably be extended to more specific fields of study. Wouldn't work all that well in a polarized society like USA, though. You'd get identical questions where the answer will depend on the party affiliation of whoever was making them. Still, in more sane countries, it could really help to expose the "charismatic bullshitters" a la Trump for what they are.
That would also probably result in younger generations not being able to advance in citizenship levels if they held different ideals from the older generations. It would almost certainly have made it hard for pro-racial/LGBT equality movements, which generally got a lot of members and support from the young, get as much steam as they did, if the opponents of such reform could just point to the low civic level scores of the supporters as an excuse to ignore them.