Lunardrift
To clarify for those below: Fluttershy is most likely the oldest(back in the cutie mark chronicles flash back she looked older than the rest of the group, or at least taller/thinner, but i'm going to assume she was older); spike is most likely 3 or 4 years behind twilight, maybe even 2 years behind(mainly due to the fact that when he was hatched she grew him up to an adult and then back, it's not hard to assume that he might not have been fully reverted to age 1, plus she wasn't that old when she hatched him, maybe 6,7 or at oldest estimate 9), beyond that dragons age differently(slower than ponies or at least they lack signs of true growth in age if their like spike)
Biggest loser