Besides going balanced, there's two popular builds for stats known as Baldr and Hank ratios that tak advantage of special gyms (the best gyms in the game barring going drug-free, which will end up net less stats if you're not chugging Xanax) - this is most often done with one defensive stat high and one low, so yesish high dex is somewhat viable
At your age it's best to train whatever your current gym is best in, as special gyms won't unlock until halfway through the heavyweight gyms, and going imbalanced early will make you fall behind quickly, usually at a minimum you want either 10m or 100m (or even 1b, depending who you ask)
Given that eventually heavies are fighting primarily either dex or def whores, both stats are important - if you only have 100m SPD it's impossible to hit anyone with over 6.4b dex (64x the opp SPD and dex sets all hit chance to 0), conversely if you have 100m str anyone over 1.4b def you'll do 0 DMG always, so really you'll need both
All this being said, you're always going to fight better with 4 balanced stats against someone of your same total stats, but the ratios would allow you to get higher numbers quicker with the special gyms, so you'll usually be better (or at least roughly equal) to those the same age/training habits of someone who goes balanced