I never was able to double tongue in high school. I put the horn away for over 3 decades after that. Picked it almost a decade ago. Did the private instructor thing a couple of times as an adult (or senior now). About 5 years ago I was asked to do one of the solo parts in Bugler's Holiday. I picked 3rd - quickly. Struggled especially where the 3rd is the entry solo (should have thought that part through - 2nd has no entry parts - does it?). Luckily we put it away for a few years. Till last week.
To my surprise I was able to keep up. Took it out to practice this week and I can apparently double tongue now.
So is that how it happens? You can suddenly double tongue? Practice over the years showed no improvement - then it ... happens?
I decided to jump to "up streaming" - I don't really know what it is but read it in a post last month. Sounded interesting - but I could not make anything work last month. Tried this week and appears I can get another 2 or 3 notes higher and lot more comfortably and a lot less work.
Maybe 2012 is going to be the end of time.