From the given clues:
- Keshav is second in height but younger than Rekha.
- Parul is taller than Megha but younger in age.
- Rekha and Megha are of the same age, but Rekha is the tallest.
- Nikku is taller than Parul and elder to Rekha.
The age ranking in descending order is:
- First: Rekha (tallest, so assumed oldest).
- Second: Keshav (second in height, younger than Rekha).
- Third: Nikku (elder to Rekha, and taller than Parul).
- Fourth: Parul (younger than Megha, and younger than Keshav).
- Fifth: Megha (youngest).
Hence, None of these are in the third position by age.