Science at higher levels is about much more than studying. Graduate school is very different than undergrad. Grades don't matter anymore, and some programs you don't really take many classes at all. You learn through independent reading of primary literature and through people you meet, as well as some classes and seminars of course.

Writing becomes supreme for academic scientists.

Also incredibly important is being able to portray confidence and work independently and be able to weather large degrees of isolation. The people who do the best (in my experience) are consumed by what they study and don't require a lot of feedback about how they are doing. That can be really tough for a lot of people--especially women.

While you get a Ph.D. which on average (in the U.S.) is upward of 6 years, that is 6 years that you will not be benefitting economically. IN science you will receive a stipend or some other sort of fellowship, at least most people do to some extent. But that will be enough to live on. And you are not investing in a retirement plan.

To then get a job as an academic professor requires 2-3 years of post-doc experience after your Ph.D. still making very little money, unless you are a superstar meaning you get a paper in Science or Nature while in grad school. You don't see money until you're an academic scientist.

If you truly love a topic of study, then a Ph.D. will be worth it. Staying in an area that has broader implications (like biochemistry or immunology or genetics for example) also means that you can leave academia and go into industry or government.

A Ph.D. is a long, hard investment. If it's something you love and can't get enough, you may be a good candidate.

Luckily, in the U.S. you probably are not too old. You will be older than a lot of your classmates. But we have a fairly liberal education system, and people who are older often do even better because they are more focused. There are speciic fellowships for re-entry students, specifically women. Check out Awis.org (assoc. for women in science) and some others.

okay...back to work for me..

If you want to find out how much biochemists or neuroscientists earn, go to the web sites of their professional organizations. I don't know what they are, but you can probably find them pretty easily. One that may be useful for you is the chemistry organization, the American Chemical Society (ACS). They'll have resources on their site about how much people with degrees in chemistry-related fields make, and statistics for women in the field, how long a PhD takes, etc.

30 years is definitely not too old. I've known people who finished their PhDs in their mid to late 30's, so you're fine in that respect.