Rivals at 16 often become friends at 30. Time takes the edge off competition.

Rivalry usually requires a small pond and a shared scoreboard. Once you are both out of that structure, the thing you were competing over turns out to have been minor, and what remains is that this person understood the same pressure you were under. Proximity made you opponents; distance can make you allies.

If there is someone you are currently sharpened against, try seeing them as a person in the same situation rather than the obstacle. You can still compete without needing them diminished. And a message to an old rival years later is received far more warmly than you would expect.