answering this is probably like wondering when it's the right time to have kids.
it's easy to define parameters like "financially independent" or "happy at work" or "both parents approve." but kids, marriage, World War II... they often just happen and then you handle it with whatever your resources are at the time.
for me, getting married was more about a decision to start the next chapter of my life, than wondering if the person i was dating was the "right one." because i loved her for years before we wed.
and for better or worse, the concept of the Right One is also kind of silly. not because your partner can't or shouldn't be the one for you. but because we have this thing called Divorce. if you really screw up a marriage, you can start fresh. and some of the happiest people i've met are once-divorced, now dating, or once-divorced, now single.
what's probably worse than choosing the wrong person, is never giving yourself the opportunity to find the right one.