In the 21st century, in several nations, most... begin a new life at universities
This sentence above is quite long. One interesting thing about language is that when we're learning it we want to master it so that we can type long, complicated sentences -- but then we discover that shorter sentences are better. That's why Yoda uses short sentences. : ) So I truly think you will always have better outcomes when you keep sentences a bit shorter and simpler. They impact the reader's mind more, because they are easier to decipher.
At the end of the first paragraph, I think you should add one sentence that succinctly expresses the main idea you are expressing in the essay. Give a sentence that expresses the most important message of the essay.
You don't have many mistakes, but you can improve the style here with number agreement:
applying for a job at an office
is an effective way.
Here is some advice about the word 'since":
The environment of the
office will provide youngsters a big chance to work with people from different backgrounds as well as obtain real experience for their chosen major at the universities. --- When you use the word 'since' this way, it must be in the middle of a sentence.
Example: Office jobs offer learning experiences, since many professionals work together.
It is better to use 'because': Office jobs offer learning experiences, because many professionals work together.
If you start a sentence with 'since' or 'because', it must be like this: Since I work in an office, I learn a lot.
Because is better: Because I work in an office, I learn a lot.
The word 'since' more correctly refers to something about time: I have learned a lot since I started my office job.
Or: Apple has never been the same since Steve Jobs passed away.
Despite these attractions, however, some drawbacks do exist. --- Great sentence. Also, it's smart that you acknowledged the opposite argument.