What's age got to do with it? Tatum is a phenomenally gifted defender. J.Brown has great athleticism & footwork on defense. Ojeleye will be back into the rotation. But who guard James is really besides the point, since he's going to use the high screen most of the time.
The key defensively will be collapsing into the paint and scrambling out to the shooters. FWIW the Raptors had a v.gifted defender in Annunoby defending James ...team defense is what counts.