I am watching Toms videos right now. The Beginner PLO part and his mathematical ones. Any more you can reccomend?

I am not playing micros so tbh I haven't watched them. Maybe someone who plays those stakes will see this and can answer your questions. 

Where would you say the cutoff is when it comes to videos still being credible, reliable sources of information - 2 years? 3 years? Less? 

I, too, download and watch tons of videos off of DC and barring subjects like math which are timeless, I generally don't like to go back much farther than 2-3 years unless it's a series of videos that's solid gold or something must see according to the community. 

The only thing that DC has for me that RIO doesn't right now is the abundance of videos for 25nl and under and the community is also full of players at these microstakes. For me, naturally a lot of the information is going to hit me spot on. A lot of the videos here at RIO are for stakes and concepts way above my current paygrade, although in just a short time I have learned a ton off of these forums and videos as well. I know I'll spend all of my time at RIO at some point down the line when I move up in stakes, too. DC can't touch you guys at the other games and the higher stakes anymore and yeah, RIO is crippling DC when it comes to new content being pumped out at those higher, more relevant levels of the game. 

Where would you say the cutoff is when it comes to videos still being credible, reliable sources of information - 2 years? 3 years? Less? 

I think it really depends on the topics they are covering. Like you said math but also basic concepts, starting hands etc. are some of the subjects that have been discussed from very early on and can/should be watched by every beginner if they are able to. Other than that I wouldn't invest too much time in older content. As for videos above your limit I would suggest just to learn the concepts and try to adequately incorporate them (at least partially) in your own game at the the limit you are playing. The most important thing is understanding the logic behind it.