Research I've read disagrees. Mostly I've read the dog literature but some of it covered dogs and cats. Some said such extremely early neuter as paediatric might indeed result in smaller growth of penis and especially in cats where the ureter is small anyway it could cause problems if there was a blockage. Other readings said no. I can point you to a list of information on neuter/spay considerations in cats....umm wait, I think I do have one that deals more with cats. Wait while I go look at the Kustritz research....
Feline lower urinary tract disease is a syndrome
consisting of hematuria, dysuria or pollakiuria, and possible
urethral obstruction and is most commonly classified
as idiopathic. The reported incidence of FLUTD
is 0.6%.134 Despite numerous vehemently declared
anecdotes of an increase in the incidence of urethral
obstruction in male cats castrated when young, numerous
studies35,132,135 have failed to detect a correlation between
gonadectomy of cats at any age and a decrease
in diameter of the urethra or an increase in incidence
of FLUTD, with or without urethral obstruction. In 1
large study,136 investigators identified gonadectomy as
a risk factor for development of FLUTD in both female
and male cats and also identified an increased risk of
development of FLUTD in overweight or obese cats. In
that study, sexually intact female cats had a relatively
reduced risk for development of FLUTD.
As you can see this one says no. But I have read others that said yes. I think how you define "young" is important. Young might mean pre-puberty for some but I'm thinking you mean paediatric which varies but might be before 12 weeks or even before 8 weeks?