Yea they grow fast. I'd say safe bet a foot after full year. If you feed raw shrimp with vitamins could grow faster. Big water changes every week or four days will help. That's big fish 101.
Mine slowed in growth at around 15 inches Ate the same amount but slowed to about .5 inches a month. 5 inches to 15 I would bet was less then a year on mine
Sorry just noticed you asked tigurnus not tiger my bad