I'm going to be 30 next year. These are probably the advice I would have given to the “20 years old me”
Don't take your failures too seriously. They are not a measure of your competency. And moreover, there is nothing better in life than recovering from failures!
What others think about you will keep changing according to situations, circumstances and your immediate environment. What you think about yourself should be the priority.
Get rid of your toxic friends. They are appealing but they are not needed.
Don't try to impress every single person. Some people are going to hate you for no reason. And it's not your problem.
Don't have any strong opinions on religion, GOD, success, wealth and people. With time, they change radically. You will be surprised.
Learn to say NO!
Always challenge conventional wisdom. Don't do anything under the pretext “because everyone else does it”
These are part of me that I just realised how much I waste my time.
Hoping my 40 I won't regret!