Is there a time limit to charge my brother with stealing from Mom?

Your mother threw you under the financial bus when she gave her money to her son. Yes, he should be taking care of her now. And she STILL won't stand up for you? That's where you are in her priorities.

All statute of limitations vary by state and by crime. Civil cases also have statutes of limitations.

First off, research if the case can still be prosecuted this long after the "crime". I use quotes because this may not have been a crime if he had consent to invest but then lost the money in contrast to outright stealing. I am going to say that this case has passed the statute of limitations for criminal charges.

Second, establish of the case can be brought as a civil suit. The statute of limitations for civil suits is often longer than with criminal and in some cases, the clock starts ticking when the act is discovered, not when it was committed.

Also, the burden of proof for civil cases is much, much lower and can also include unintentional acts.

I am going to suggest that you not get your hopes too high. I doubt that a case can still be brought at this late time and I also doubt that a case could be won based on what little information you have provided.

Call Adult Protective Services in GA, first. However, it kind of sounds to me like it may be too late to do anything. From what I have read about others experiences on here, the system isn't much help.
Now, regarding her current situation and help for you, does your mother not receive SS checks every month? That should go toward her care. You can call the Area Agency on Aging and get information about what services are available, ie, rides to appointments, adult daycare, etc.

The way I remember it, Mom (currently 84 yrs old) allowed him to invest her life savings. Dad had taken care of investing till he (2008) passed. She never wanted him to steal her money. Obviously!(duh me!) She was grief-stricken-- her husband had passed away and her son took over the investing before he returned (later that week) to his home in Atlanta.
We live in Kansas. I am not quite sure how I ended up taking care of Mom. She had to sell her house quickly and at a loss (because her life savings was gone and she could no longer afford to live in her home) and had nowhere to go. So, we took her in.
Yes, I think it should be his job to take care of her. He will not answer the phone, will not return phone messages, and when I email him, his wife replies via email and calls me all kinds of rude names. (She's not very nice.)
I've printed the emails out and have shown them to Mom. She has never stood up for me before and I know she will not do so now.
I wrote to the newspaper "Money Manners." They wrote back very quickly and suggested I get legal assistance. I need someone to walk me through the process of pursuing legal action against him. I've never been in this kind of a situation before!
I'm starting a full-time job soon and I don't know how I'll transport her to appointments and exercise class while I'm at work.
I have to take the keys away soon. Should do it tonight, actually. Everything costs money and I don't know what to do. My friends don't have this experience yet, so no ideas there. Thank you!!!!!

Did mom give him access to her accounts? Was she mentally competent at that time?

If she was fine with him taking care of her funds, then why are YOU taking care of her?
Shouldn't that be his job?

An you prove that he coerced her in some way?