I'm mid 60s also on Lantus & Humalog (and anticoagulant) - if I'm swimming (most days) I reduce Lantus dose on day before by 1 unit - same with pre-swim Humalog. Eat approx 2 hours before swim, aiming to have BG around 7 at start of swim.
During swim I drink carb drink ('high five') which has...