Alma 56

Stripling means -

"A boy our young man, even suggesting slim or thinness"

Thus, Helaman calls them -

"...my stripling Ammonites..."  (Book of Mormon | Alma 56:57)

Based upon Helaman's writings, I perceive these young men being somewhere between the ages of 14 - 18 years old.

After their first battle, Helaman writes -

"...Now they never had fought, yet they did not fear death; and they did think more upon the liberty of their fathers than they did upon their lives; yea, they had been taught by their mothers, that if they did not doubt, God would deliver them.
48 And they rehearsed unto me the words of their mothers, saying: We do not doubt our mothers knew it."  (Book of Mormon | Alma 56:47 - 48)

"...Thus were the Lamanites pursuing them with great vigor when Helaman came upon their rear with his two thousand, and began to slay them exceedingly, insomuch that the whole army of the Lamanites halted and turned upon Helaman." (Book of Mormon | Alma 56:52)

And then -

"...the people of Nephi, the people of Antipus, and I with my two thousand, did surround the Lamanites, and did slay them; yea, insomuch that they were compelled to deliver up their weapons of war and also themselves as prisoners of war."  (Book of Mormon | Alma 56:54)

And now the miracle -

"...it came to pass that when they had surrendered themselves up unto us, behold, I numbered those young men who had fought with me, fearing lest there were many of them slain.
56 But behold, to my great joy, there had not one soul of them fallen to the earth; yea, and they had fought as if with the strength of God; yea, never were men known to have fought with such miraculous strength; and with such mighty power did they fall upon the Lamanites, that they did frighten them; and for this cause did the Lamanites deliver themselves up as prisoners of war."  (Book of Mormon | Alma 56:55 - 56)

I couldn't help but ponder that these "boys" "fought as if with the strength of God; yea, never were men known to have fought with such miraculous strength..."  So miraculous was this that they "frightened" the Lamanites and they gave up.a