Tamarind definitely does not take 10 years to produce from seed, at least in my experience. My mother planted some seeds about 4-6 years ago, kept one and gave one to my grandmother. Ours fruited last year and has lots of flowers now, and my grandmother's fruited even earlier.
I too am curious as to what the normal duration is from fruitset to maturity, and perhaps cultivation or NPK formula advice.
It was a bit surreal reading through this thread this evening during a search for tamarind growing posts, coming across the above comment, and nonchalantly glancing at the username only to realize it was posted by myself.
After a decade or more, we are back to our previous house whereat my mother had also planted a different seed-grown tamarind than was referenced in my above comment. To my recollection, this tree is also part of the triad of trees grown at our last home and my grandmother's house. In either case, I am reviving my previous comment to see if anyone has an update on my original query about fertilizer recommendations?
Unfortunately, after being torn down by a severe hurricane and losing most of its main trunk, as well as being neglected in the years we were living elsewhere, the tree here has not been flowering nor fruiting discernably for the past year or two at least. I have recently repainted my thumb green and undertaken an effort to revitalize our fruit trees, and today purchased and broadcasted some Sunniland 6-1-8 fertilizer around the root zone, however I would be happy to hear about other fertilizer suggestions.
Pic is from April 2021, about 1.5 years after Hurricane Dorian which uprooted nearly the entire tree:
You can see the remnants of the original trunk laying horizontally near the ground, and the offshoots which have since taken over to form an upright 'U' of main branches on either side of the original trunk's base. The upright main branches are now about 10+ feet tall and have lots of healthy-looking foliage, but no flowers nor fruit. I am also toying with the idea of hard pruning the tree to bring it down to a more manageable height, and purchased a hand saw along with the Sunniland fertilizer, but would not be sure how best to approach the task given my limited experience.
In total, the tree should be 15 or more years old by now, and I suspect the lack of flowers and fruit may be a fertilizer issue as the other same-aged seed-grown tree I originally referenced at our previous home still has unpicked ripened pods hanging from its branches. We have extremely sandy soil if that helps with fertilizer recommendations, and I am in the initial works to have bulk wood chips trucked in to begin the process of amending the yard with additional organic matter.