Protagonists that age during the game

[Lone Wolf Leonhart]

Ocarina of Time

Breath of Fire III

Tales of Graces f

What are some games you've played where the heroes age during the journey of the game?

[Fynn]

Dragon Quest V. Probably the absolute best example of this, actually.

Fable

[Vermachtnis]

Rune Factory 2, maybe? The second half of the game you play as your kid.

[Wolf Kanno]

Fallout 3 - From the cradle to the grave... quite literally actually...

Lufia 2 - To a lesser extent, you start as a teenager and become an adult with a family halfway through the game.

SaGa Frontier 2 - Multiple times actually with different characters.

Suikoden Tactics - Start as a kid and grow up to be an obnoxious immortal teen.

[Lone Wolf Leonhart]

Suikoden Tactics - Start as a kid and grow up to be an obnoxious immortal teen.

Hah, that's right.

I love this one, actually. It was my first Suikoden game and it made me want to go out and get IV so I could spend more time with these characters.

[WarZidane]

Horizon: Zero Dawn, The Last of Us - granted in both of these all of the aging happens very early in the game, but there is some gameplay pre-aging.

Beyond: Two Souls

Assassin's Creed 2 and 3

Fire Emblem Genealogy of the Holy War (which by the way has a pretty dark story for that era of JRPGs), Fire Emblem Three Houses

[Fox]

Final Fantasy XV!

Tales of Berseria to a small extent...

Yakuza.

Of course, most of these are simple one off time-skips with some narrative impact but little mechanical change. I'd be really interested in seeing games with aging more meaningfully aligned with the mechanics. A few games have done this over the course of a series, like Metal Gear Solid, but few do so during the span of one game.

[Ayen]

The only ones I can think of is Ocarina of Time and Beyond Two Soul.

[Lord Golbez]

Breath of Fire II also

[Mercen-X]

In Fable 2, age is a consequence of a particular path along the light. However, as my ex-girlfriend pointed out, the aesthetics could be easily reversed (first with hairdye which is unrealistically permanent). I chose the evil path just to be a deck (I think it was sacrificing someone? A woman or a child, I don't remember)
Also, don't you go from being adolescents to teenagers in Lunar?

[Lone Wolf Leonhart]

Also, don't you go from being adolescents to teenagers in Lunar?

Adolescent is basically just another word for teenager. The stage between childhood and adulthood where puberty happens.

[Jinx]

When they came out? Like, none.

When I spent most of my time playing it? FFX, I was 16 at the time, Rikku's 15, Yuna's 17.

Sadly, I'll never really get to experience that again because I'm about to turn 28, and that means I'm a hag by Japan's standards.

[Vincent, Thunder God]

Ryo ages in Shenmue - just very, very slowly.

[Fynn]

Also, if you want to get technical

The Sims (2-4)

[Lord Golbez]

If we want to get super technical about slow aging, probably just about every protagonist ages during the course of the game, if not explicitly, except for rare instances like Suikoden protagonists with true runes.

[Lone Wolf Leonhart]

If we want to get super technical

We don't.