Time is an illusion, I don't see why time dilation would not be possible. Sometimes I feel like some days of real life are shorter than others. Have you noticed how time went by so much slower when you were a kid? Time perception is just that, it is not some kind of accurate clock. Although it may be unlikely that you can spend 100 years in one dream, maybe if your brain fills in enough gaps with fake time it may be possible.

Personally, I'd say that I haven't really experienced time dilation, my dreams have lasted around the time of a REM cycle. Even dreams where I have spent days felt more like days in a movie - condensed into an hour or so. I don't see why it wouldn't be possible in theory though.