I'm a 54-year-old beginner. I started going to the gym twice a week last October. I'd like to increase that to three times a week, and the personal trainer I had for a few months (who's no longer available) suggested a push/pull/legs regimen when I was ready. I work from home on Monday, Tuesday, and Friday, and go to the gym on Tuesday and Friday now, so I was hoping to add Monday. All of the "beginner push/pull/legs" plans I've seen suggest a rest day in between each, but that timing doesn't really work for me. Is it a good idea to do the PPL on Mon/Tues/Fri, or am I setting myself up for problems or injury?
Rest between different muscle groups is not necessary. What is essential is is adequate rest and recovery between training of the same muscle group. Your split stated there has you doing one PPL cycle every week meaning you have 7 days between each workout of the same muscle group. That is perfectly fine, of not ideal, for a beginner. From what I've read and also confirmed through my own experience, you need 5 days between chest workouts, 3 days for arms, and 4 for everything else. I train on a 6 day cycle with only the sixth day being a rest day. I'm perfectly able to train on 5 out every 6 days because it is set up so I have the necessary rest between for each muscle group as stated above.