You definitely don’t need a 120K+ income job to do philosophy. That is a thing which could help, but it’s a very soft, optional prerequisite. And generally if you’re successful with philosophy, you’ll prefer to get your income from it, so you won’t want the job anymore.
A 120K job has downsides. Those kinds of jobs tend to take up a lot of your life. You may work on some weekends. You may think about work at home. You may choose some hobbies that are adjacent to the job. You may make friends with coworkers who are into the job topic and some adjacent stuff but not philosophy. The job may stress you out or require a lot of mental energy. A lot of those jobs are knowledge work. Or if it’s physical work that pays that well, that’s probably hard and tiring too. Or if it’s a relatively easy, unproductive job at some kind of upper-middle management, say, then it probably requires a lot of attention to office politics since other people will want that job too, fight you for promotions, maneuver to get credit for everything good and blame others for every bad result, etc.
Anyway, the more you set up your life without philosophy, the greater the risk that you make a bunch of mistakes with long term consequences. Getting married before having reasonably stable philosophy views is a risk. So is long term dating. So is choosing a job. So is learning a field.
An undergraduate degree that you finish at 22 has risks but, big picture, it’s not that bad (if you enjoy it; if you hate going to school then it is that bad). You’re still young at 22 and have reasonable flexibility (particularly if you have little to no debt – significant debt is a big problem). A PhD you finish at 27 is considerably riskier. Now you’re a lot older and have done a lot more committal stuff. It’s a much bigger deal to go do something that doesn’t use your PhD than to go do something that doesn’t use your undergrad degree. From age like 18-30 (very roughly; it varies) is a pretty crucial time period when you’re a young adult with some freedom and flexibility. By 30, most people have their life path pretty set (including people who don’t choose a career; they usually don’t seriously start pursuing a career later either; if you’re pretty directionless at 30 you’re likely to still be like that at 40). An undergrad degree uses up like a third of that 18-30 time frame. A PhD uses more like 70%.
People often don’t realize how much they set up their life as they do it. They don’t realize how much they’re structuring their interests, hobbies, friends, and everything else around some lifestyle that makes it hard to change.
College provides you with the opportunity to develop a social/career network. That’s different than providing the network.
If you go to class and do what you’re supposed to do, you’ll get a degree and some skills, but will not get a network. A useful network takes some extra actions on your own initiative.
Networking also involves stuff like choosing who to have in your peer group and who not to. It’s somewhat committal. You’ll tend to be influenced a lot by your peer group. You’ll tend to become and stay more similar to them. It’s part of how you choose your path in life. So if you study stock broker stuff and network with finance bros and get that kind of job, you’re probably going to end up one of them, not a philosopher. You’ll drift away from philosophy the more you fit in with that other stuff. You’ll choose hobbies, interests and many other things in ways that are compatible with the finance life rather than developing and selecting them in philosophy oriented ways. To be really good at stuff, you need to arrange your life so a bunch of stuff indirectly supports and reinforces it, and other stuff doesn’t clash with it (not a 100% hard requirement, but it’s unrealistic to expect greatness otherwise). By far the easiest way to do that is to start doing something early – e.g. by age 20 (though 10 is better) – so it’s already part of your life first when you add a bunch of other stuff to your life. Changing later is hard because there’s so much intertwined stuff to change, much of it only indirectly related, and no one thing is a hard blocker but there are a lot of things and they add up, and you don’t want to change half your life, and even if you did want to that might not work out well.