As someone with some time in corrections, I would suggest the following to you:
Get a pair of handcuffs.. and a 14-year-old..
Tell the 14-year-old they are to "resist" being handcuffed to the best of their ability, without actually hitting you.. twist, turn, trip, run, crawl, etc.... anything goes..
You, on the other hand, are prohibited from using anything other than "necessary force" to restrain him/her...
Now, from a "standing start", let's see you handcuff that 14-year-old..
Good Luck..
I and three (3) other adult males, when in my mid 20's, and in probably the best condition of my life, attempted to restrain and cuff one (1) man in his 20's as a training exercise...
He was a friend, and a fellow officer, so we did our best to "overpower" him and force him to cooperate..
We were not "easy" on him, nor were we overy zealous or brutal...
Even outnumbered 4 to 1, he managed to resist for quite a while.. possibly as much as 5 minutes..
One on One is practically impossible unless you have a major physical or psychological advantage over the subject..