If I could do it all again

Recently, I have a friend who has started his PhD study in a prestigious UK school. There's also a new Korean guy in our lab who has started his PhD candidature with my advisor. Coincidentally, both of them are in the age group of 30-32. I don't know what strike a chord in me, and made me think back of the days when I first started my PhD. Those memories seem vague at this point. I do remember the chaos and confusion at not knowing what is in store for me, and knowing that I knew nothing about the work that was ongoing in the lab. I remember that I had to read the papers that were related to the microarray work that was initially my research topic. And I could not understand perhaps 50% of the content. I remember that I felt like snoozing when I read those papers. And I remember the days of thinking I'm not cut out for it.
If I could do it all again at this current age, how different would it be? This is the question that I have been asking myself recently when I saw these two fellow embarking on their PhD. I think it takes big courage to step into this long and arduous journey at this age, although strictly speaking, we aren't really that old. But I guess the answer to my question is I am not willing to do it all again when I am 30 years old. It's too long a stretch, and no end to the tunnel. The truth is: I'm still trying to find some light in my tunnel.