I am now in my twenties!

This week I had my 20th birthday and was asked, by quite a few people, if it felt any different. Even though my "age" has gone up a year, I'm only a day older than I was yesterday. Should I really feel much different?
Traditionally, twenty-one is considered a much bigger milestone than twenty but what can't you do at twenty that you can at twenty-one? Adopt a child? (which I don't want to do now anyway) fly a plane? (where would I get the time and money to do this?) become an MP or a counsillor? get sent to prison?
I think becoming twenty is a much bigger change than twenty-one. I'm no longer a teenager, I have now been alive and breathing for two whole decades, it's the beginning of my twenties! I am even getting jokes from people about being an "old git" and how it's all downhill from here! Although I don't think there's anything I can legally do now that I couldn't at nineteen.
It has made me realise, even more so than I did before, how short life is and how quickly time goes by. Every year time seems to speed up, which is really scary. When you're a child the days are so long and the summer feels like a year, now a day seems to disappear a lot quicker. I don't know if it's because we have more responsibilty and more worries than we did as children or if it's simply the way life goes, the course of nature.
I do feel some sadness saying goodbye to my teenage years because I don't know if I lived them to the full. I didn't enjoy all of my years as a teenager (but I think it's rare if people do) and I feel a bit like I was held back by certain things and missed out in some ways. On the other hand, so far, I'm finding my twenties very fun. I know it's only been a few days but there is still an optimistic part of me that hopes for happiness.
Generally I think you are always the same person, no matter how old or young you are, but with age you gain life experience and therefore wisdom. I think I am a lot less naive than I was a few years ago and I'm also more mature, but I still enjoy being silly (who doesn't, really?) because I'm still me, just a bit older.