How do I make my thesis into something debatable?

My working thesis is the psychological reasons for hoarding and the mental effects on the children and families of adult hoarders. How do I stay on topic with this but write a debatable paper on this?

Although a thesis statement should be on a debatable topic, the thesis itself should have a firm stance and try to defend one side of a debate. I do not think your paper should try to tackle both of these subjects, unless this is what your professor/teacher is expecting. You should have strong arguments that either support or refute the subject, while still touching on the opposite side of the debate. Always include the other sides arguments but make sure they don't overpower your argument. Make sure you can always disprove them. I would need more information about guidelines and background to help you further. I hope this helps a little bit at least.

I need to narrow down "life" to make a thesis

Life is a very general topic, so you have to break it down into pieces .
e.g.
Life
different aspect of life
Happiness

From happiness you can further extend your thesis to what makes a person happy in life. Such as, friend, family, health, security or even wealth and power . And from there you can add on to each of these factors to form an essay.

That's the way I usually appoarch a very general topic, hope that helps! Good luck!