I used some Light DME as a starter about a month and a half ago. I only used part of the bag, and I ziplocked the rest of the bag’s contents. Is the DME still good or do I need to buy a new bag before beginning another starter?
DME can last quite a while, a few month is no big deal if it was in ziplock bag. You are good to go.
If it’s sealed off from moisture, it will last a VERY long time. I brew from grain, but keep DME on hand for a boost sometimes. I’ve used DME that was more than 2 years old with no worries and no ill effects.
How well it’s sealed is the key.
+1 That stuff can turn into a brick if it absorbs moisture.
+1 on the stuff turning to brick, but even then it’s still good for use. Break off pieces until you have the quantity you need.
Although I mostly just use it for making starters, I’ve used DME over a year old with no apparent ill effects. I’ve also used DME that has turned into a brick, and although I now am more carefull about keeping it tightly sealed to avoid the inconvenience, it still worked fine.
Another good use for ‘bricked’ DME - eat it like hard candy. 
