
In my personal experience of two bitches I know really well, yes!!!
the first is a golden Retriever bitch who was spayed at six months, and even now with arthritis she is still mentally a puppy, and can't wait to rough and tuimble with my latest pup, as each of my adults has outgrown her. Unfortunately I could not let my youngest 0play with her until she was grown up, as Ruby just didn't know how to realise that she couldn't play that way without hurting herself (she tore a cruciate, with mad playing at 9, not my dog thank god).
A bitch that I bred comes to stay with me, and was spayed after her first season, quite aerly at 10 months. It was very noticeable when she stayed this year, that at nearly five she still acts as she did at a year, and even my Jozi, who has always been a brat is more mature than her, and I feel that she is very mentally immature.
On the other hand her half brother who was entire until 3 years of age is just like his entire half brother, a proper man.