Who was the youngest ever player to win a tournament on ATP Challenger Tour?
We had similar question about ATP World Tour. I thought that knowing answer to a similar question about challengers might be interesting, too.
As far as I'm aware - the youngest Champion of a Challenger Tour event was Michael Chang when he won a Challenger event in Las Vegas in 1987 when he was 15 years and 7 months old. Not that surprising considering he also won the French Open at 17.
From what I remember hearing also - Richard Gasquet was pretty young when he started winning Futures and Challengers as well - while he was 16 I think.
I'll try to find some sources to back up my claims and come back here and edit this answer afterwards.
Two sources found by Martin (in the comments)
Youngest ATP Challenger winners
The following list contains the youngest Challenger winners since 1991 including one colum denoting how many main draw tries (i.e. qualifications are not counted if the player did not qualify for the main draw) the player needed.
Winner Age Try Year Tournament Richard Gasquet 16.04 1 2002 Montauban CH Bernard Tomic 16.34 3 2009 Melbourne CH Rafael Nadal 16.8 9 2003 Barletta CH Felix Auger Aliassime 16.84 10 2017 Lyon CH Novak Djokovic 16.99 2 2004 Budapest CH Juan Martin Del Potro 17.1 9 2005 Montevideo CH Alexander Zverev 17.17 7 2014 Braunschweig CH Jimmy Wang 17.26 7 2002 Fergana CH Nicola Kuhn 17.31 2 2017 Braunschweig CH Rudolf Molleker* 17.58 3 2018 Heilbronn CH Casper Ruud 17.69 1 2016 Seville CH Evgeny Korolev 17.71 14 2005 Aachen CH Tomas Berdych 17.82 9 2003 Budaors CH Nick Kyrgios 17.83 2 2013 Sydney1 CH Borna Coric 17.83 8 2014 Izmir CH Mario Ancic 17.85 13 2002 Belgrade CH Denis Shapovalov 17.89 9 2017 Drummondville CH Nicolas Almagro 17.89 2 2003 Olbia CH Mikhail Youzhny 17.89 7 2000 Samarkand CH Taylor Harry Fritz 17.94 2 2015 Sacramento CH Donald Young 17.98 15 2007 Aptos CH * added manually
The fantastic dataset by Jeff Sackmann is used (available here). Last Update of this list: 21.05.2018