By the time we are twenty, we are expected to be entering adulthood with confidence and competence. While we are gaining independence and learning how to take care of ourselves, it seems that we are also expected to learn how to take care of others too. While this is all a part of "growing up" I believe that your twenties should be your most selfish years.
Being a twenty-something year old most likely means you are on your own for the very first time. You no longer need to depend on someone, so you should take this chance to enjoy an independent lifestyle before becoming someone else's dependent. You need to experience life before you take on the job of caring for another's life. You are responsible for yourself now, so it is time to get established: get a steady job, make a cozy home for yourself etc.
As for relationships, maybe you had a stereotypical high school relationship, maybe you've casually dated, but it is certainly not the time to tie yourself up in a commitment. Although you may be #adulting and being a successful member of the real world, you are still ~finding~ yourself in your twenties. Just because you think you are so much more mature, wiser and THINK you know what the hell you are doing doesn't mean you do. Just because you aren't the same person you were at 15, or 17, or 19 doesn't mean that you won't continue to change throughout your twenties. Let yourself continue to grow; don't plant roots, let the wind carry you. By all means go on dates, meet cute boys but don't take anything too seriously.
Things you should take seriously: your education, your career, your health, and most importantly: yourself! Worship yourself. Treat yourself. Respect and honor yourself. Make sure the people in your life do the same. It is not selfish to grow past those who are stuck among the weeds. If removing toxicity and pettiness from your life is wrong, I don't wanna be right. Find people that not only like the same things as you, but have similar goals, and also want to grow.
Take time for yourself. Go on a solo vacation, stay in a hotel with big fluffy pillows and order expensive room service. Go to the beach with a picnic and enjoy the sunshine (wear sunblock!) Buy a cookbook and cook every single recipe and then master one so it can be your signature dish. Don't feel compelled to attend every social event in your calendar. It may seem like everyone your age is graduating from college, or having a bridal party or having babies, but it doesn't mean you have to go to every single celebration; there will always be more. You aren't missing out.
Allow yourself to be as free as you can, all the while setting yourself up for your future. After all, you won't be in your twenties forever, someday you will have to turn thirty!