Pros:
-Not many people are used to Young Link level of camping
-Even fewer are used to Young Link's ability to go in
-He's usually even or wins with floaty higher-tiered characters
-His game plan of projectile-into-aerial can be used the entire game, as it's also his kill set-up
Cons:
-His 5 worst matchups are the 4 best and 5 most common characters in the game
-Apart from Marth & Falcon, his worst matchups are very difficult to win unless you face an inexperienced opponent. Marth & Falcon are just "quite difficult".
-He's pretty easy to combo and kill for most top tiers
-He lacks options compared to many other characters (EX: he almost doesn't have a grab)
-He probably isn't viable outside of local-sized tournaments, and even then, he's very difficult to win with at a local scene
-He doesn't really play like any other character, and probably isn't the best character for getting good fundamentals with, making you stuck with Young Link with potential difficulty in player growth.
I love Young Link, but I personally do not consider him viable as a solo main (I secondary YL).