On avodart (dutasteride) for 5+ years to treat bph. decrease in penile length observed. connection? if so, will stopping meds reverse this unfortunate side-effect?

No it is not related: Avodart (dutasteride) is a 5 Alpha reductase inhibitor that will reduce the size of the prostate and lower the psa level by 50% .It may lower the volume of the ejaculate and caouse ed in some men but shold not change the length of the penis.

Weight gain: Have you gained any weight? Avodart (dutasteride) will not make your penis smaller but gaining weight will definitely make it look smaller.