A PhD is a real job that counts as real experience when you apply to industry jobs. Develop your own machine learning model in the process of completing your dissertation? Sure, you may be "entry level" in the private sector, but it's not going to be a low wage "entry level." You won't be "behind" people who were working in industry all along.

Know that PhD experience counts as "work experience." At least it does in the field I'm getting into, which is in biostatistics (so not yours, but may certainly have enough similarities that the same "rules" apply).

Somebody convince me why it is good or bad to finish in 3 years, and if 30 is late to start "real life"?

If you want a PhD, you need great grades and research experience. It's much easier to make this happen on a 4-year plan.

Also, I have a secret I'm going to tell you: You've already started "real life." It is not a simulation. What you are doing now, whatever it is and wherever you are, is the real deal. Living in your parents' basement eating cheetos? That's "real life." Traveling the world? That too. Feeling like a child who has no idea what they're doing even though you're actually a full grown adult? Yep. That's life. And this whole not believing that "real life" is now thing never stops. At least it hasn't for me, and I'm in my late 20's. I graduated school and the thing that you think of as "real life" wasn't as great as they make it out to be (although the increase in money was nice), so I went back to school and will eventually get my PhD and will most definitely get it after I'm 30. Oh, and all of my "real life" experience was in a different field than I'll be getting my PhD in.

Computational neuroscience is a very niche field that requires graduate training. Everyone in your field will likely be your age or older when they "enter" the market. Some people may choose not to get a PhD, but it's their loss because computational neuroscience is cool and their missing out! Again, I was out of school for a few years and it sucked. I would not give up this path for the world.