Do I need an attorney if the person is coherent to enact an Irrevocable POA?

Why would they want to enact if they can make their own decisions?

As long as a person is competent, they can enact an irrevocable power of attorney. They’re rare and usually used for businesses. It wouldn’t be a bad idea to consult an attorney.

You need to look at the Irrevocable POA document itself as that should state how to enact the I-POA or when the I-POA goes into effect.  Also, you need to review the POA laws for the state that the I-POA is written in and effective in.  Each state has slightly different laws, regulations and guidelines regarding POAs.