When did 18 become the "legal" age in the US?

Did such an age actually exist before 1970? To avoid the massive pandemonial confusion such a question usually creates, I do not mean drinking or voting age - simply the age at which one is "presumed" to be legally responsible for himself.
 
The draft age has changed back and forth and isn't really a good indicator for this either.
Facts:
1917 - Selective Service created. Males 21 to 30 register.
1918 - Age limit raised to 45.
1920 - Draft discontinued.
1940 - (1st ever peacetime draft) Males 18 to 65 register. Males 21 to 36 drafted (not yet in the war).
1941 - Males 18 to 45 drafted (now in the war).
1948 - Males 18 and up register. Males 19 to 26 drafted.
1951 - Males 18 1/2 and up drafted.
1973 - All-volunteer armed forces created.
1975 - Registration eliminated.
1980 - Registration reenacted for males 18 to 26 "in case" a draft becomes necessary.

Like with everything else, having one age for all is always going to be hit and miss.  For the states I've lived in (all along the left coast), you can drive alone at 16; buy cigarettes, buy spray paint, have consensual sex and die for your country at 18; then buy and consume alcohol at 21.  Needless to say, it's not hard to find examples of people that are still unfit to be driving at 21 or that can use spray paints responsibly far younger than 18.

It is not uncommon in the US to try 14 year olds as adults in criminal courts, sometimes subjecting them to the same punishment as real adults. The laws in some states allow even younger ages, as low as 10 in Kansas. Presumably that indicates their fellow citizens consider them to be legally responsible for their actions. Using the draft age as a measure of responsibility is bizarre. Military service is demonstrably the social structure that requires the surrender of the greatest amount of personal responsibility, and shields the person from most moral consequences for actions performed as a result of following the orders of others.

I'll never forget this! When I was young the legal drinking age was 21 and when I turned 21 they changed it to 18!!! I REALLY felt cheated. (I think they have since changed it back to 21).
I also remember "military beer" 3.2% alcohol, I wish I could buy it today. You could drink that stuff ALL day and feel good. To drink beer all day and not get drunk these days you have to be an alcoholic. I just enjoy drinking some beer but I don't enjoy getting drunk.
Then there are all the different "age of consent" laws. Some of our great great grand mothers were likely married at 13 or 14 years old.
I think military ages change according to needs. In Germany in 1945 they were taking 12 year olds and 60 year olds into service. I just missed being drafted to go to Viet-Nam (I still have mixed feelings about it.. I am thankful and respect all who went and I think they were treated shamefully when they returned, not by me but truthfully, I was scared at the time and saw no threat to my country but I saw a threat to me.. anyway, it is hard to understand much less explain). The first year I was eligible I think they changed it to only 21 year olds just before my number came up. The next year they ended the draft just before my number came up. I "rolled up".
I was 120 pounds soaking wet and would no doubt have been put down into tunnels. I'm happy to be here but like I said, I am still confused about what was going on at the time. On one hand I wish I had volunteered, knowing what I know now. On the other hand, the person I was then was just there for the party. I was never into politics until I got older, then I figured out that it is all just a scam...
 
Legal age.. hmmm. IDK, I imagine it is arbitrary until push comes to shove. Now where can I get some 3.2 beer?
 
J

The night of my high school graduation in 1973 (In Minnesota) the drinking age changed to 18, though not until midnight. We had one hour in the bar that first night. I was still 17 but my older brother let me use his ID.  I was then in the military before I turned 18. The only thing significant about all this is that it was some fine memories.

In Finland there's regularly discussion about dropping the driving lisence age from 18 to 16.
We have a lot of sparsely inhabited country side, where moving around can be very difficult for younger people.
Then they use the "cancer of motor traffic", the so called moped cars that have a speed limitation of 40 km/h.
You can guess how folks love those road plugs.
 
We don't have much police cars on the roads, so in the country side you can drive very carelessly without getting caught. That's what people are afraid of - that the 16 yrs old have even less self control than the 18 year old. We've gotten our traffic casualty numbers down to a very acceptable level, and many would not want to risk that development. Also, cars, traffic insurances and gasoline are very expensive here, which means the youngsters have the poorest and most unsafe cars.
 
At 18 you're an adult here. You can drink, vote, be elected, be sentenced...

webbs hill studio
Interesting your comment about the lack of police in the countryside.
I live in the country in the first state in the world where every police car is capable of random alcohol and drug testing as well as mobile radar detection.
 

It's not only the countryside. I live 25 km from the centre of the capital, Helsinki, and my job is located in an 
industrial suburb, about 10 km from the centre. I can drive to work and back for two-three weeks without
once seeing a police car. There are cameras here and there and such, but it's the economy that's made them cut police resources year after year.
The last time I was in a road block (which usually includes mainly alcohol/drug testing every driver) was
three-four years ago.
 
In northern Finland it's normal having to wait for police for an hour or even more. The closest car may be over 100 km away.
Then taking a person to the jail may require 2-3 hours, which time the car is  off alarm duties.

robert_e_bone
...the part of the human brain that deals with things like 'evaluation of consequences of behavior/action' is not even present in the brain until the early 20's.
Bob Bone

Funny. I think I developed that around 6 or 7. Not bragging or anything..... just always getting in trouble.... usually not my fault though.
 
So what I'm hearing is there is no "official" age of adulthood. As opposed to:
1. Draft age (which only applies to men anyway)
2. Drinking age
3. Voting age