What they don't understand about growing up is probably the fact that when you wake up on your birthday, you're still the same person as you were the day before. Nothing's really changed but the day and people's expectations towards you. They wish you to grow, but they don't know that you still are 5, 9, 10, and 15 at the same time on your 18th birthday. It's natural.
That's more than a self-defense. In times when you don't feel so good, you can always say that its okay to cry or to be scared like when you were 5. Its alright to sink deep down into your own imagination, seek for a little excitement, and get back to reality when you're tired, just like when you were 10. Its alright, you should never let anyone harm you by their judgments. You are as free as anyone else, and you're fine that way.
To grow up is to learn. You learn that you need to fall before you can stand, and you understand that all that it takes is to get back up again every time you fall. You learn that it doesn't matter how many bruises you have, sweet moments are still sweet. Another thing about growing up is to appreciate. You might not always feel good about anything, that's the way things are created. When you feel negative, you're able to see positive things. And vice versa. You hear it million times that life does give people lemons. When you appreciate all negative things in life, you're growing up.
Enough with the theory. There are times when you're forced to be all grown up. You need to be strong in order to make others feel strong too, even in your weakest level. When ages are just numbers and those who have grown up feel like being 3. When you see the need to shed others' tears from your watered eyes. You need to think clear when everything doesn't seem to make any sense. You may hate the situation but there's no escape. To grow up is the only hope, to forgive is the only way.
There are times when you hate people who taught you to love. Think of all the gloomy memories to remind you how far you've gone, and think of all the sweet memories to remind you how happy you could be. You need not to worry, I've learned to appreciate and I've grown so strong that I got your back.
Ps: focus on your thesis and good luck for that! I'll try to figure out other ways so that everyone doesn't need to cry anymore.
(Song quoted above is Lenka's Sad Song)