There's a list of all Paizo playable races, and none of them go smaller than Small. The shortest is the halfling; the shortest halfling (according to the "random height" table) is 2ft 8in which is 81.3cm.
For third-party races there is the kval which is size "tiny". The shortest kval is 10 inches (25.4cm) tall.
For not too much money (3040gp total, I believe) you could pay a ninth-level wizard to cast a permanent reduce person spell on you, cutting your height in half again.
An eighth level druid can take the form of a Diminutive animal for eight hours, and can do this three times per day -- so essentially you could be a Diminutive animal forever if you wanted. For example you could be a thrush which is around 20cm long. If your intent is to play a dedicated spellcaster this is not a bad tactic (though the inability to speak might cause problems).
Humans aren't as bad as you think
Firstly, humans gets +1 to all stats, in the PHB (pg. 31):
Ability Score Increase. Your ability scores each increase by 1.
This means, as @SeriousBri pointed out in a comment (now deleted), they can get higher starting stats when using the point buy system. But even with rolling for stats, if you end up with a bunch of odd numbers, this can increase all of the modifiers by one.
(To quote a player at an RPG club I go to, after rolling either mostly or entirely odd numbers: "Well... looks like I'll be going human!")
Secondly, the variant human rules (which I believe is AL-legal, as far as RAW goes). They get +1 to two stats, plus a free skill proficiency, plus a feat. This last point makes them very strong (depending on what feat you're going for).
From the PHB again, page 31:
Variant Human
If your campaign uses the optional feat rules from the Player’s Handbook, your Dungeon Master might allow these variant traits, all of which replace the human’s Ability Score Increase trait.
Ability Score Increase. Two different ability scores of your choice increase by 1.
Skills. You gain proficiency in one skill of your choice.
Feat. You gain one feat of your choice.
As an example, making a Barbarian or Paladin or something who uses a great weapon, you can pick the Great Weapon Master feat, which allows a second attack (as a bonus action) if you crit or kill something. This is essentially Extra Attack at level 1, which is very strong.
Furthermore, it's possible for a human using the variant rules to have a 20 in a stat at level 1. As an example, elves get +2 to Dexterity, so if they roll an 18, they can have a 20 in Dexterity at level 1. However, recently a player in a game I'm playing in rolled an 18 as a human wizard, put that in Intelligence, used one of their "+1 to any two stats" to make that a 19, then took the Linguist feat (which, among other things, gives +1 to Intelligence) to increase that to 20.
Ok, so they don't have darkvision, but neither do Dragonborn or Halflings.
Best Answer
There are guidelines for creating playable races in page 285 of the DMG, however, it doesn't go into detail on creating Large races, specifically (nor do they really go into detail on making medium characters, mechanically, save for the 'compare to other already-established races' approach). This is largely because playable races are only sized between Small and Medium (4 to 8 feet tall).
Take a look at the Goliath in the Temple of Elemental Evil player's companion, the Minotaur and Centaur race in their Unearthed Arcana version, and the final version of Minotaurs and Centaur in Guildmasters' Guide to Ravnica, all these races sound like they should be Large. In fact, if you take a look at page 223 of the Monster Manual, you'll find that Minotaurs are Large creatures, despite this, playable minotaurs are Medium. Of course, you could argue that the Krynn minotaurs who don't dwell mazes have evolved to be smaller. Then again, who's to say it wasn't a design constraint? ;)
So, why aren't there Large player-characters?
Weapon damage dice
In page 278 of the DMG, you can see rules on damage dice of creatures. A Large creature is going to wield oversized weapons, this means their damage dice are doubled, tripled for Huge, and quadrupled for Gigantic. A Large PC with a Glaive will be dealing 2d10+str, almost doubling the damage output just by being large, at 1st-level.
Area
A Large creature occupies a 10x10 ft area, making it more of a threat in battle especially when it comes to blocking and generally being a 'presence' in any encounter.
Aura Areas
As mentioned in this tweet by @ThinkingDM, auras emanating from Large PCs cover more squares than Medium PCs. Specifically, for a 5' aura, Large PCs cover 12 squares versus the Medium's 8 squares. In 10' auras, Large PCs cover 32 squares versus the 24 from Medium.
Squeezing
In order to accompany any typical adventuring party, a Large PC will need to squeeze in most places a typical adventuring party would visit. Whether it's a tavern, a forest gnome's tree house, or a mine tunnel made for dwarven miners, a Large PC will be continuously at a disadvantage while squeezing through most other terrain a Medium creature would have no problem fitting in.
These traits, inherent in the creature's size alone, make a Large creature fairly overpowered in most any game.