What is the career roadmap for a physicist? How does one find money for living expenses during studies?
I was trained as a physicist, and slightly changed direction towards theoretical physical chemistry during my PhD.

Money depends on where you are in the world. Some places have scholarships or state funded loans. In addition to that, I have taught physics and math at almost all imaginable levels, everything from high schoolers cramming for exams, to TA'ing at my university. Money becomes a bit easier when you get to the PhD, as most places will give you a salary or a grant you can live off of. 

I married at 22 and had my first kid at 24. Way before any of my classmates and later colleagues. At the time people asked how I would manage my career having kids so early. I thought it was nice to be able to have the flexibility of a student when she was a baby. Now the same people are struggling with post docs and a lot of travel, with infants at home. 

I got my Ma at 27 and PhD at 31, making me slightly older than average. This does not bother me too much. I have seen people graduate with PhDs being 10 years older than me and do fine. Although they have to face some negative bias going through the hiring process for junior positions.

I still learn new things all the time, and even though I have the relevant degrees, I don't consider my training as a physicist done. It probably never will be.

What to take from all this?

There is no perfect time to graduate. If you want to study, study, no matter your age.

There is no perfect time to marry or have children. But wait for too long, and it might be biologically challenging.