My male sugar glider is a few months over a year old and is only 90g. Is this too light for a male? He is quite active at night and he usually eats most or all his food. He's fed on the sgs 2 diet.

Here is link to weight for sugar gliders, your glider is at the lowest of range.
http://www.sugarglider.com/gliderpedia/index.asp?Weight

Your diet plan for you glider does not look familiar to me, sorry I don't know anything about it.

SGS 2 is mostly used in Europe for practical reasons (somehow it is really difficult to find some ingredients used in most diets over here which leads to always have to make complicated operations to substitute)

The weight also depends on the size of your glider, mines never go over 95gr, and the 95gr looks a bit fatty (our gliders seem to always be a bit smaller than their US counterparts).

Basically, if his weight is stable, that there is food left in the morning and that he is normally active, it's likely to be his normal weight. If however this weight is the result of a change or that you notice any oddity in his behavior, or lack of activity, then it might be a good idea to ask a vet to make a few tests to see if there is no parasites or underlying disease

I personnaly chose to not use SGS2 because I have reservations on the overall "fruits and veggies color system" based only on individual ratio...

While the ratio is a nice indication, it doesnt tell you which amount of calcium and phosphorus each fruit and veg really contains, and even by picking up only things in the green list, the overal ratio of the mix can be really low (papaya for example has a really good ratio, but in fact contains really few calcium/phosphorus, so the other things used can totally reverse the proportion).

Marie Bannister created and used this diet for over a decade with good result, but the same outcomes applies only if everyone uses the same fruits and veggies as she does, in the same proportions (and we all have our preferences when it comes to pick up fruits and vegs).

Another point of concern is that it is never said that sweet potato must be cooked before serving, which is worrying.