It is often argued by some nations that by the time a person reaches the age of 18, he/she can function as a responsible adult, while others disagree with this statement by saying that this age bar should be increased. Personally, I believe that an individual is, in fact, fully mature and has the ability to make sensible life-decisions by the age of 18.
Firstly, it has been proven that 18 is a reasonable age yardstick. To be more specific, many psychologists, through their extensive research, have concluded that a person can fully function as a responsible citizen by the time he/she reaches the age of 18. For example, many countries such as India and Sri Lanka allow a person to have alcoholic beverages at the age of 18. It has been proven that any person below this age limit had not acted responsibly when the same type of drink was consumed. That is why I firmly stand on the side that 18 is a reasonable age to allow a person to act like an adult.
Secondly, in many cultures, 18 is when a person moves out to live on their own. In other words, the average person starts to attend college at the age of 18, and this is coupled with moving out of their parents to live independently. For example, I moved all alone to the US from Sri Lanka when I was 18, and I would proudly say that I was mature enough at that time to differentiate between what is good and what is bad. I drove responsibly, studied well, and got good grades in all my freshman year classes, and drank alcoholic drinks responsibly. This is why I believe that 18 is a very good age for someone to start living as an adult.
In conclusion, I strongly believe that anyone at or above 18 years old is fit to function as an adult since it has been proven by research that 18 is a good yardstick. In addition, many young adults make their way to college and start living independently when they reach 18. 
It is  
often
 argued by  
some
 nations that by the time a  
person
 reaches the  
age
 of 18, he/she can function as a responsible adult, while others disagree with this statement by saying that this  
age
 bar should  
be increased
.  
Personally
, I believe that an individual is, in fact,  
fully
 mature and has the ability to  
make
 sensible life-decisions by the  
age
 of 18. 
Firstly
, it has  
been proven
 that 18 is a reasonable  
age
 yardstick. To be more specific,  
many
 psychologists, through their extensive research, have concluded that a  
person
 can  
fully
 function as a responsible citizen by the time he/she reaches the  
age
 of 18.  
For example
,  
many
 countries such as India and Sri Lanka  
allow
 a  
person
 to have alcoholic beverages at the  
age
 of 18. It has  
been proven
 that any  
person
 below this  
age
 limit had not acted  
responsibly
 when the same type of drink  
was consumed
.  
That is
 why I  
firmly
 stand on the side that 18 is a reasonable  
age
 to  
allow
 a  
person
 to act like an adult. 
Secondly
, in  
many
 cultures, 18 is when a  
person
  moves
 out to  
live
 on their  
own
.  
In other words
, the average  
person
  starts
 to attend college at the  
age
 of 18, and this  
is coupled
 with moving out of their parents to  
live
  independently
.  
For example
, I  
moved
 all alone to the US from Sri Lanka when I was 18, and I would  
proudly
 say that I was mature  
enough
 at that time to differentiate between what is  
good
 and what is  
bad
. I drove  
responsibly
, studied well, and  
got
  good
 grades in all my freshman year classes, and drank alcoholic drinks  
responsibly
. This is why I believe that 18 is a  
very
  good
  age
 for someone to  
start
 living as an adult. 
In conclusion
, I  
strongly
 believe that anyone at or above 18 years  
old
  is fit
 to function as an adult since it has  
been proven
 by research that 18 is a  
good
 yardstick.  
In addition
,  
many
 young adults  
make
 their way to college and  
start
 living  
independently
 when they reach 18.