I think this is good advice, except probably for road cycling. Both my physio therapist and Yoga teacher told me that sitting on a road bike is counter-productive to improving my flexibility, given that I already sit at a desk most of my day. Especially the hips will stay in the same angle for a prolonged time.

Edit: if OP is concerned about damaging their untrained musculoskeletal system, then swimming is a low risk activity to get started with sports.