It has always been tough for me to really define what New Age actually is. But that seems permissible, for it is no easy for two New Agers to define it either. It seems to just be a sort of spiritual and metaphysical eclecticism, and so it can take as many forms as there are people that adhere to “it.”
Of course, I have met people who think they are spiritual because they “eat a lot of fruit” or do yoga while reading the Bible. New Age seems to me to be a mixing of error with error, or sometimes truth with error. But if truth is one, no mixture can be permissible. If we have one “mathematician” who says that 4+4 is 8, and another who claims that 4+4 is 10, do we have an eclectic math when we say 4+4 is 9? Or when we say it can equal 8 or 10? No, we either have it right, or we have an erroneous math.
I have heard some New Age followers who are at least a little more learned try and claim that, for instance, the Catholic Church has Franciscan spirituality and Carmelite spirituality, etc, and thus, a similar trend. But this is obviously a failure to grasp differences in the way a life geared towards truth can have different emphases rather than a split personality (or split truth) disorder that is objectively what happens with the New Age movement.
To emphasis works of mercy or contemplation in life, all according to the one true God, cannot be equated to accepting the teachings of Jesus, but also worshipping many gods (or none at all) in a mixture of eastern and western mysticism. One can say that Jesus and Mohammed and that the tradition of the Vedas and the Brahmans all have good uses, but to turn this into a mixture of the truth of Jesus along with the truth of the others is merely to muddy the water when seeking purity.
One of my favorite modern authors, on the subject of the philosophy of religion as well as other things, is Peter Kreeft. I have done little real study of New Age outside of personal experiences with other people, but listening to several of his lectures has at least helped develop my understanding to at least an elementary level.
I know that many New Age thinkers will place someone like St. John of the Cross in their “camp.” I have to say that, a relative of mine who is deep into New Age thinking did send me, as a gift, a copy of the works of St. John of the Cross, and I am thankful to have been able to add it to my library. But obviously, she and I have very different interpretations of what the holy Carmelite meant.
Like any group of people, you have well intentioned souls and you have ignorant and even very strange people in all camps. Often I find that, rather than try to see exactly what they believe, why, and how this came to be (although all of this effort can truly be a labor of love) it is simply best to present the truth boldly as it truly is and let its own weight take hold if it be the will of God.