The average age of AA for New Hampshire is like 25. Baseball-reference says Borucki is 1.4 years younger than average, and he was born March 31st, 1994 (23 years old). Pannone is 9 days younger, born April 9th of the same year. So a little under 25 I would say.
Smith Jr. is 24 (turning 25 in October) and he is 2.7 years younger than the average. So you are looking at like 27 or 27.5 being the average age in AAA.
Pannone will not be a top prospect, but he's a LHP starter, something the Jays did not have really at all besides Borucki and Perdomo. Seriously, those two are the only LHP the Jays have in the top 30 at all, and luckily both are still starters right now. There are some LOOGY's in the system throughout, and a few more LHP starters/relievers who can stretch a bit, but Pannone gives the Jays something they lack.
Taylor is just a wildcard guy. He's young and has done decently well. Jays have some middle infielders, but when you are young, position does not really matter as long as you can play everyone.