Lucid dreaming has a time frame or window?

[imj]

As the title says....because I myself have been doing it for 6 years straight and have noticed a 'pattern' where people on here have reported that they were able to lucid dream regularly like say within a year or some within a few months of practicing it. I compare those who have successfully made their lucid dreaming proficient in a short time and kept it that way without much effort as compared to myself. I have put in the full attention and effort into lucid dreaming but out of the 6 years...the first 3 years were the most promising as it had the most active frequency of lucid dreams like sometimes one a month or 2 a month and by the time it hit the 3rd year it had plateaued to none or just one after many months and then normal dream frequency started to deteriorate in the 5th year and then dream vividness and dream frequency were greatly diminished in the 6th year. I also feel that my mind has been weakened over the 6 years and affected the dreams..so my query about this finding is that there may be a window or time frame within which one must fulfill proficiency before the dreaming mind 'runs out of gas'. IMJ