Younger and older is a relative term with Yoda. The best lifespan of a human is pushing 90. Yoda is upwards of 900 in ROTJ ("When 900 years old you reach, look as good you will not."), which means that "Yoda years" is kind of like "dog years" - 1 human year=10 Yoda years.

Assuming he's exactly 900 in ROTJ, his equivalent human age is 90 at that point. That makes him somewhere in the 850 to 880 range over the course of the PT, which puts his equivalent human age at 85 to 88. Can you really tell the difference between an 85 year old man, an 88 year old man and a 90 year old man?