2.25" per month is up there in the champion domain; not impossible/unbelievable at all IMO - most keepers report from 1' (slow) to 2' (fast) in the first year - and IME too.
I understand your mild dismay: starting from 2"-3" to 24" in one year is ~1.75" a month - this is often professed as a max growth but there are some claiming higher numbers. Plus, the growth spurts have to be thought of - the OP speaks of only 7 months; so it could still average 2" or below for a year. Also, in the extreme, one can take it further and quote a monthly growth during the wildest spurt of say 3"-4" in that month... but of course, this is not representative of a long(er) term growth.