There is nothing wrong with those weights at those ages. Yes avacodo can be given as treats now n then, I feed it to mine about once a month maybe.
I have 11 gliders in my house right now 10 are mine 1 one is a medical foster.
Cozig 5 month about about 75-80 grams good weight for this glider
Amy 3 yr ol 68 grams ish not
a good weight for this glider
Nicky 3 yr ol 200 grams not
a good weight for this glider
Simon 7 yr ol 164 grams ( he is not overweight) good weight for this glider
Lemmy 4 yr ol 130-140 grams good weight for this glider
Leela 3 yr ol 89 grams or so good weight for this glider
Pico 2 yr old 85 grams she's dropped a few grams but still not
an unhealthy weight for her
Danzig 1.5 yrs old 80-85 grams good weights for the whole cage
Cocoa 3 yrs old 80-85 grams
Joey still nursing prolly about 30 grams I didn't weigh him today
Cage four Good weight for him
Hansel-mature adult age unknown 165-170 grams
Weights vary, just like with humans, the body type, body size, weight all that varies.
So you can have one glider that is say 3 yrs old and weighs 85 grams , and another glider same age, different body type weighs 95 grams. 85 grams for the first glider is a very healthy weight for his body type. 95 gram glider looks and feels underweight despite being heavier than the 85 gram glider. The 95 gram glider should be in the 120 gram weight range....if the weight loss was gradual,and explainable I wouldn't worry, but if it was a drastic unexplainable weight loss like a matter of weeks or days I would go see a vet. But see how just looking at 2 gliders are so very different and what might be an ideal weight for one glider may not be for another.
If the glider feels healthy, not bony or skinny, there is no need to stress about them gaining weight.
The danger weight zone for an adult glider is 50-60 grams. Even for a small framed adult glider this is the scary zone. This is when they will either live or die and that line is very very thin.
It's heart wrenching to see an adult glider in the 50 gram weight zone smaller than some 12 week oop joeys ready to go to their new home. It can bring even the most hardened human to tears trust me.
Personally, I'd say keep feeding your normal diet consistently, avocado is fine in moderation. Start a weight journal. Weigh the gliders once a week, same time of day every time I usually weight at 2 pm BEFORE snacks. Plenty of time for their food from the last feeding off the plate to digest so you get a more accurate consistent weight chart. After a while you will see who is fluctuating and who is staying constant. A few grams up or down is nothing to worry about. If you weigh yourself 4 times today it will probably fluctuate too
Anyway you will see what their "normal" is which will make it easier to tell if they don't look like their "normal" and may need vet care.
If YOU still feel your glider is underweight, look at everything, is there food aggression, is he/she acting different, do you think it needs to go to the vet, etc.. fecal test the glider to make sure it's not a parasite issue .......
One last thing about the Glider Crack, if a glider truly needs glider crack and is indeed underweight, rapid weight gain can mask a potential medical issue letting it go undetected longer. Don't fix and hide the symptoms, address the actual cause, then there is no need for glider crack.