Asansa, The Lotus Position, Impossible? Options

Have been sitting in asana for a good few yers now, basically corss legged and yet after all this time I still can't manage to sit properly for more than a few minutes. Can basically do a 1/4 lotus, not a full half, leg on upper thigh but its fustrating. Sat comfortably the other day and realized that its the essence to a good practice, all that shifting and shuffling during the MP or general meditation just dosen't cut it... throws everythnig off. Main thing I'm trying for now is a full lotus, a stable position that keeps the back straight and energy flowing for an undisclosed period of time.

Can anyone here do the full lotus? How did you achive it and how long did it take?

Peace
.M.

Thank you very much for the new information fatherjhon. Also the links from Aunt Clair were very useful. I was aquainted with the fact that I'm too old for correcting the spine but I have to do something to avoid worst things. I was afraid I wouldn't be able to achieve stillnes of body but hopefully I will get to that.