Mohsin Khan struck a 114-ball 102 in what was the only century on a day the ball dominated proceedings in swing-friendly conditions.
Namibia, who are automatic qualifiers for the tournament proper by virtue of finishing as the highest Associate nation last time, were never in the game. They were all out in just over 30 overs with left-arm seam bowler Shaheen Afridi showing fine rhythm by taking three for 18.
New Zealand, on the other hand, suffered a couple of early setbacks against Zimbabwe and were struggling at seven for two.
Skipper Boshier's fighting 113-ball knock was supplemented by efforts from Todd Watson (53) and Jokob Bhula (30) as the team posted a total of 220.
In reply, Zimbabwe seemed comfortably placed at one stage with 132 for four before Boshier shone with the ball to ensure there were no early setbacks for New Zealand, who are looking for their maiden title in the U19 CWC as they prepare to host it for the third time.
Meanwhile, West Indies, who are the defending champions did not have to stretch themselves against Papua New Guinea, who just about crossed the three-figure mark.
Jeavor Royal, Alick Athanaze and Ashmead Nedd grabbed two wickets each, leaving Bhaskar Yadram to finish it in quick time with a 23-ball knock of 37.
"This was a good opportunity for us as a team to get out here and practise as a team, and play a game as a team before the tournament. We just want to take one step at a time; one game at a time. We don't want to rush anything, we got past this one and now we are onto our next one (warm-up match) which is against Zimbabwe," West Indies captain Emmanuel Stewart said.
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