I would suggest warming up before every interview. Talk to a friend or talk on discord--either about the job or just anything in general. It helps me to phone someone and chat and go out of my way to talk to people (like in stores) before a job interview. Would definitely suggest that. Try to schedule the interview to give you time to warm up. Also, consider applying to companies that you're not interested in, just to get experience interviewing. I recently had a long string of interviews. Some weren't too hot but others went really well (just got an offer yesterday!). I'm in my mid-20s and have probably interviewed around 100-150 times now (mostly phone, but also many in-person). Even when I was working, I still practiced interviewing. I think after a while, you just get used to doing it and it no longer becomes a huge ordeal.