Of course is possible to develop mediunity when you are adult.
A lot of tecniques, to develop mediunity, exists, but, the real way to develop it, is Walking, walking in the Path of Light, loving, and purifying your self, from the things that make you mediunically blind and deaf.
To Walk, without tecniques, will result in the developmente of mediunity, but, to practic all tecniques of the world, but, without to Walk, will not work.
The guy that has already born with mediunity, also needs to educate and to harmonize it, them, all are in the same level, the development is an obligation to both groups.
All persons have the same mediunic potential inside them, and, if some has born with that mediunity, more developed, well, karmic and dharmic questions, that does not have importance. And, of course that, to born with developed mediunity, not always is dharma, much times, are a severe karma.
All have the right to develop the mediunic vision, audience, etc., such as we see, we listen, etc., our dimension, but, the question is, "why wish you to this?" If the reason, is to recover something that has been yours, but that you lost, in past incarnations, perfect, but, if the reason, is curiosity, or to have "psychic powers", of course the reason is not good.
Alexandre
Sacred Space Mitch Ham Ell
http://www.mitchhamell.com.br/