Uh, obviously there is no age to rulesystems. They are either good or bad.
Chess for example saw its last change in 1880, when the rule of en passant became official - a rule invented in the 16. century and already commonly used.
D&D is designed for pen and paper, not for computers. Which is why many things are like they are. Thats probably the "age" you talk about. But that was the case in 1999-2002 when BG originally came out, and that will still be case if there will ever be a Baldurs Gate 4 from someone.
Also technically the newest version of D&D is from 2024. Not that BG3 would use that.
