ok, here’s my personal opinion…
it was incorporated in order to offer consistency to the legal system. It must, at some point in the not very distant past, have been concluded that children below a certain age, on average, were not very good at making safe decisions/ correct judgements / legal use of / etc. in specific circumstances. It was then decided to make such actions illegal if performed by persons below a certain age, making it a whole lot easier for the legal system to function (i.e. to protect society as a whole).
I personally feel that people below the legal age, who might be more capable/mature/safe/etc. than others, have to wait a bit longer in order to legally perform these actions and therefore might not be too happy with the concept of a “legal” age. Heck, i was a way better driver at 17 than most people above the legal age will ever be. But i guess the concept of a “legal” age makes it easier for the system to determine competency of an individual, rather than treat each case individually.
Also, the probability that a person below the “legal” age makes an incompetent decision might be considered unacceptably high by the legal system. The law thus preempts any damage that might be caused if such persons are allowed to perform these actions.
E.g. Let’s say the legal system determines the following:
The probabilty that an average 13 year old at the wheel will cause an accident is extremely high. This probability is greatly reduced by the time the average person reaches 18 years of age. Hence, we determine that the legal age requirement for a person seeking a full valid licence in <insert countrt here> is 18 yrs.
Ofcourse, my theory covers only things that might cause direct physical harm. So let’s say you’re asking about why an 8 yr old can’t legally watch a graphically violent film. I guess that this is because in such cases (as opposed to cases discussed earlier) the law seeks to protect young persons from being adversely affected by the content of said film. Again, apply probability theory here. Determine that an 8 yr old watching a graphically violent film will have a high chance of experiencing recurring nightmares. Determine, also, that when this average 8 yr old turns 18, he/she will be aware of the consequences of watching such a graphically violent film, and therefore can make a competent choice based on sound reasoning and is consequently personally held responsible for the choice he/she makes. So, if he/she watches such a film at age 18+ and has recurring nightmares as a result of it, that was his/her own judgement call.
ok…i’m just rambling… but i hope you get my point… lemme just re-read the question…
ok… about the progression bit… i assume there would have been a progression… an evolution, so to speak, of the laws… if the law makers realize/determine that a specific legal age for a given action does not fit in the current scheme of things they will (and have done so in the past) change the age limit… this is progression… laws that hold true today might be changed tomorrow… this will be further progression… so while it was legally/morally/socially accepted in the past to marry off a 14 year old, “western civ.” today deems it to be unlawful. This is “progression” too. Perhaps parts of the globe still legally practice child marriage (I know it happens in my country, even though it is now illegal). So, basically, legal age is determined by law makers to protect the system as a whole.
i shall stop rambling now… i don’t know how much sense i made… i need coffee…
for the mods: even though this thread may evoke more opinion than fact, i think it rightly deserves to stay in GQ, because it has a factual answer. We just don’t “know” it. yet. Also, the opinions stated could lead to a summation of the facts.
for the rest: please feel free to applaud my beautiful theory.
i should stop typing further now… because it is illegal to drink and derive at any age 