i've been doing this a long time...generally speaking, the younger age groups are not judged as harshly. my opinion is that there is nothing wrong with this. a 15 year old can take a "beating" when it comes to scores. 8 year old's not so much. they would quit in droves if they did to them what they do to the older kids. it's all part of the process.
I don't think it's fair at all, but gymnastics isn't fair anyway (glad to see my instincts are vindicated a bit though). If my 11 year old L5 who started gymnastics at age 9 is scored more harshly than her 8 year old teammates, it doesn't seem fair to her, especially when she feels she performs better. I'll be honest though, she doesn't get too worked up about the scores, she just states it matter-of-fact. She is aware that older gymnasts are subtly treated differently than younger ones. She has even commented that the head coach "loves the cute little ones". It is not too obvious or done intentionally, and dd is still getting excellent coaching, but it's there and she knows it. Maybe it's the cuteness, maybe it's the potential for greatness (certainly an 11yo L5 will never make elite), the personality, size, whatever. I am not in any way trying to take away from the hard work and accomplishments of younger gymnasts, it is just that the sport is designed for them.
I don't think judges do this on purpose, but I see them smiling hugely at these cute wonder-kids. I don't blame them - it is certainly more amazing to see an 8 year old performing a beautiful tumbling pass than a 12 year old, I usually smile all through their routine too! I don't think this consciously changes their scoring, but with such a subjective sport, I imagine it can affect it.
In all fairness, I agree with another poster than noted the opposite at lower levels. Certainly in L4 it seemed like the older kids scored better - they were in better control of their bodies; some of the younger ones were landing on their heads in the BHS or had sloppy form. However, in L5 it seems reversed. The young super-stars who will be L8 by the time they're my daughters age are clearly better than most of the field and deserve the higher scores. I'm more talking about subtle difference, nothing too obvious.
So, yes, I think the older/bigger/taller ones are judged a little more harshly, but I don't think it's done on purpose. It is what it is, for better or worse.