Ela tem que ser 24 anos mais velha. De a transcrição
RIVER: Funny thing is, this means you've always known how I was going to die. All the time we've been together, you knew I was coming here. The last time I saw you, the real you, the future you, I mean, you turned up on my doorstep, with a new haircut and a suit. You took me to Darillium to see the Singing Towers. What a night that was. The Towers sang, and you cried.
RIVER: You wouldn't tell me why, but I suppose you knew it was time. My time. Time to come to the library. You even gave me your screwdriver. That should have been a clue.
Ela claramente passou os anos completos da 24 lá (e é por isso que The Doctor veio em primeiro lugar). Eu acho que o que te confunde é porque ela não parece mais velha. O que não sabemos é como o rio envelhece. Lembre-se de que ela já teve energia de regeneração e possui algum DNA do Senhor do Tempo. De Um homem bom vai à guerra
VASTRA: [snip]Now, I have a question. A simple one. Is Melody human?
DOCTOR: Sorry, what? Of course she is. Completely human. What are you talking about?
DORIUM: They've been scanning her since she was born, and I think they found what they were looking for.
DOCTOR: Human DNA.
VASTRA: Look closer. Human plus. Specifically, human plus Time Lord.
Em outras palavras, é perfeitamente possível que sua fisiologia única a mantenha jovem.