igtheog9987:
Responding to each of your questions:
Q: I am considering asking my coworker who is 2 years my senior to give me an LoR. Is this a good idea?
A: This is fine. It's always better if you can have a supervisor, manager, etc. write one but sometimes that is not always possible. As long as this person has seen your work up close and you can trust them, you should be fine. You might want them to position themselves as more of a superior than a co-worker to the extent they are comfortable with that arrangement.
Q: Would there be any cons to it?
A: It's the exact opposite of what we said above. If they are viewed more as a "friend" it could look like someone is doing you a favor. If they aren't close to your work, the recommendation might seem thin.
Q: Or should I ask a more senior person to help me out?
A: Again, if you can get a more senior person that would be great. Just make sure they are someone you can count on and someone who knows you/your work well. If that's not viable, stick with your 2-year older co-worker.