It's more his size and maturity than age tbh. A 2016 might be pushing it (depends on when 2016) but if he was fed and cared for well I can definitely see him hitting proper weight and being ready breed within several months if not now, again depends when they were born (aka how much time they've had to grow) and how they were cared for (growth is maximized in ideal husbandry conditions). And then there's the less predictable factor of individuality; some snakes will reach maturity early and some will take their time, just like humans and really any other animal out there. I've heard of 300 gram males breeding and I've heard of 1000 gram males not being mature enough-- of course those are extreme examples but you get my point. A safer bet would be a well-started 2015, as most should at least be up to size by now unless they had issues starting out.
Also-- breeding a pied to a hypo will give you all normal looking babies, no pieds or hypos or hypo pieds unless the parents are hets for each other's homozygous traits. They would all be double het for the traits pied and hypo though, so going that route you'd have to raise up and breed the double hets together to even get a 1 in 16 (or 0.0625%) chance per egg at hatching a hypo pied; it's likely you'd be trying for many years before you hit the odds. In my opinion it would be more economically productive (and less frustrating) to just buy a pair of visuals that also carry the hets you want, like a pied het hypo and hypo het pied, as it would speed up your project by literally years and exempt you from feeding and housing all of those double hets for however many years it takes you to hit your double recessive. Even just one parent carrying a het will speed up the project considerably.