With a quick Google search of dating/relationships in your 20s, it appears that the internet would vote that you should be single in your 20s because you need to find yourself and because you should be out there being young and fucking around (I mean that multiple ways). I can't and don't dispute the points brought up in the articles I've read, however, I'd like to present an alternate view, and say that I think it's okay, even good, to be in a serious relationship in your 20s - yes, even your EARLY 20's.
The number one argument for being single in your 20's appears to be that your 20's is your time to start being independent and to really figure out who you are and what you want out of life. You're looking for a place to live, you're starting your career, you're making new friends, you're figuring out hobbies or whatever adults do because you don't have to study for exams anymore.
I also believe your 20's is a decade a remarkable growth. When you age from say 60 to 65, you may not see much of a difference. Likely the same house, same job or retired status, same chair you sit and read your book in, same bedtime. But when you age from 20 to 25 or 25 to 30, big things are happening. You're starting a job, maybe switching paths, and you're deciding whether you'll want kids someday, and you're traveling which gives you a new perspective on life at home and what you need to be happy.
If you're single you may be doing some soul-searching, spending time with yourself, journaling, taking classes, delving into your career, etc. I should point out that I too have time to journal though I am in a relationship but I'll grant it that single people may have more time, not being obliged to maintain a relationship. However, I think there's a lot of learning about yourself that can be done while in a relationship, perhaps ONLY in a relationship.
A relationship involves team effort and conflict resolution and to do either you need to look at not only what you want from your partner but you have to look at yourself through your partner's eyes. I've learned in what ways I can be selfish, and I consciously slow myself down and look at how I'm behaving in the relationship: are we both getting what we want out, are we both putting equal effort in.
I think a lot of people run when the butterflies in your stomach stop or the sex begins to slow down. People don't know how to cope with the end of the novelty, they don't know how to enjoy the day-to-day and love the person in front of them. I would rather learn how to love someone and learn how a relationship should progress before I'm older, potentially getting married. I would rather risk argument and heartbreak now then divorce later.
Relationships also come with the obvious perks: steady sex, compliments, fun dates, free dinners (sorry guys), no awkward pauses when your relatives and co-workers ask if you're seeing anybody. But the lesser known ones are honestly better. If you're with someone you love, they inspire and encourage you to be a better version of yourself, you want to be better for them and you can be because of the energy and the love they contribute to your life. You feel more free to fall and take risks in other areas of your life (school, career, friends) knowing that you have a partner who will be your anchor.
I suppose my advice to a 20-year-old would be explore, explore, explore. Whether that be yourself or the world around you. And you're free and capable to do this exploring by yourself. But if you have a willing travel companion, he might just point out things in your explorations that you wouldn't have seen with just your pair of eyes.
Video: Single Vs. Relationship - Debatable