Ok, fair enough. Then why don't you answer his question listing these practical differences with something that is not "One had to learn magic and the other was born able to do it", which is frankly mechanically irrelevant.
Admittedly I'm not exactly up to date with the nuances introduced in 5th edition, but as far as I know the main difference between mage and sorcerer (aside for relying respectively on INT or CHA as main stats) has always been that the former has access to way more spells and more powerful ones in relation to the current level, while the latter can use more spell slots per-day before resting.
I suppose my fish/human example wasn't clear enough. A fish isn't just able to swim, if it's not swimming it's a dead fish. And here about sorcerers:
People with magical power seething in their veins soon discover that the power doesn’t like to stay quiet. A sorcerer’s magic wants to be wielded, and it has a tendency to spill out in unpredictable ways if it isn’t called on.
Source -
https://www.dndbeyond.com/classes/sorcererYou also can read there
https://www.dndbeyond.com/classes/sorcerer#DraconicBloodline how exactly Draconic ancestry affects a Sorcerer.
And here is about Wild Magic - http://dnd5e.wikidot.com/sorcerer:wild-magic , which basically makes your Sorcerer a walking disaster.
