Isn't it true that younger athletes perform better at sports?
At the elite peak of specific sports, yes. But 'better at this moment' is not the same as 'you're done.' Most athletic careers span decades, and you can be both slower than you were at 25 and still selected, still competing, still performing useful work that younger players can't yet.
If I can't keep up with her pace in practice, doesn't that mean I should step back?
Keeping up in speed is not the only measure of athletic contribution. Experience, decision-making, body awareness, and recovery strategies are things younger athletes acquire, not things you lose. You might move differently, but different isn't disqualified.
How do I know this isn't just me making excuses for declining performance?
Track one objective thing: consistency over a season, not a single sprint. Recovery time, decision accuracy, game situation reading, or injury prevention over weeks tells you more than one practice against someone ten years younger. You're not weaker for adapting to a different timeline.