Is really long poo (feces) normal? (slightly longer the size of a pencil)

Yes, unless change: Bowel habits have a wide range of 'normal'. Frequency may be twice daily to energy other day. Comsistency can be loose (not watery) to firm (not hard). Length can vary (pencil length can be normal) as can diameter. Shape can vary. Color can be from dark tan (not chalky) to dark (not black). Most important issue regarding 'normal' is if there is a change in pattern for over 1-2 wks, then c ur doc.

Yes: Verying lengths of stool are common.