I should probably know the answer to this question but I am looking at putting a small subwoofer in the youth room at my church “Not a very big room” such as the PROEL - EX12SP. My question is I have a 1980s Peavey Mark V M-3000 power amp laying around and I would like to push the sub with it. Is this possible being that the amp is so old?
There may actually be several aspects to this and one of them is your goals. You didn't mention what the rest of the system or how it is used and it is not clear what you hope to achieve by adding a subwoofer. With a stated frequency response of 55-160Hz (no limits given), a sensitivity of 96dB/1W/1m and a power rating of 150W continuous and 300W peak (no idea why the peak is just twice the continuous), the EX12SP may help if you have small mains but would seem limited in the potential benefit to many systems.
Another aspect is how you plan to wire everything. That includes possibly addressing a single sub with a stereo system and how you plan to low pass the subwoofer and high pass the mains. The EX12SP has an internal passive crossover that provides a low pass for the subwoofer and a high pass output for the mains but it is passive with the typical application being a sub between the amp output and each associated main. The 160Hz corner frequency of the internal crossover is again probably more appropriate for very small mains and may also suggest using a separate crossover for other situations, however the low pass, 12dB/octave aspect for the subwoofer also cannot be easily bypassed, so you may have to consider that. In any case, you'd have to figure out how to make the single sub with its internal passive crossover work in your system.
Assuming you make all the above work, then you have an 8 Ohm, 150W continuous/300W peak rated speaker and an amp that clips at 130W RMS into 8 Ohms (1% THD, 1kHz). So it may not be a bad match, but that goes back to the first question of what you are trying to do.