Depends entirely on the skater. Some boots last a long time because the skater is overbooted, which isn't a good thing. Other skaters are "hard on their boots" i.e. they put a lot of stress on their skates which causes them to break down faster. Or the boot is mis-fitted - too wide will break down faster.
We will get about 18 months out of an underbooted Harlick, skater 165 lbs, doing double A and triples and skating roughly 20-25 hours weekly about 48 weeks of the year - because this skater is not hard on boots due to the landing technique, and because, frankly, they're custom so they put extra strength where the "wear" was on the previous boots. No growth issues at this point, which is great.