I wanted to toss this out there: I finally went to the hospital for plastic surgery for generation 5 (she's an Immortal), because I wanted to shave her weight down on a permanent basis.
I did check age pre and post op. She went in at 76 days; she came out, and was still at 76 days (when my Immortals have their bars reset via Ambrosia, it gets reset to 69 days).
I don't know if I was just lucky, or if it's been fixed, and I plan on sending her back because she's still blimping (so I can check the age thing again).