One agency told me it would not be legal for my mom to sign a POA because she wouldn't remember she did 5 minutes later. Another agency has told me that as long as she can recognize me, looks to me for support and advice, and seems to understand what she is signing at the time of signing it then it would be legal. She is in the mid stages of dementia and is going to need my assistance with most everything pretty soon.
If mom has a diagnosis of dementia on record, you could face a serious and possibly successful challenge to a newly executed POA even if it seems to the attorney that mom is fine.
Mom and I went to our local Elder Law Attorney, she wanted to change a few things in her will and also explain why she was doing it. I wasn't allowed in there during her meeting, it had to be ALL her and no me, just in case siblings would say I was prompting her. All of that was noted in the affidavit, very detailed.
So yes, go do it now!!