Hi, for me your post is really heartening. I am married with two little kids. It seems like right now I am passing through toughest period of my life. I work online under strict deadlines and pressure. So basically, I am doing one full time job (of managing my family, in-laws etc-etc) another full time job (online work is not easy, trust me on this, especially when you little ones have taken this huge responsibility of constantly disturbing and distracting you!!) and studying for CSS. I have given my first attempt, waiting for result. This is my last chance, reason same as yours, 27 years age limit.

But I believe that I can do this, I can actually crack this exam.

I would not suggest you to quit your corporate job. Although I don't know about your financial position, but, whether you are able to pass through CSS or not, you will need this job to finance your PhD. I would suggest you to be realistic. Let's see how things are unfolding. Trust me, unemployment is very pressurizing. Just imagine, your bank balance (if any!!) quickly thinning and nothing to back on.

Try and manage your job with your dreams.