My groomer told me that it's better to take them in when they're young so that they get used to it. Yoshi had his first haircut at 5 months. I actually spoke to a few different groomers before I decided on THE ONE.
I had Yoshi scheduled as the first one in, so that he could be the first one out. I also asked them to call me as soon as he was finished so that I could come pick him up right away. I didn't want him stuck in an unfamiliar crate too long. I brought his favorite ducky blanket, a chew toy & a soft toy. It's a good thing I brought a blanket, because the place I brought him to didn't have any padding on their wire crates. They must have thought I was NUTS! But I was sooo nervous.
They ended up doing a great job, Yoshi was a good little boy & now I have a great relationship with our groomer
Just be sure to tell them EXACTLY how you want his hair cut (in a respectful way, of course). I've read some horror stories about grooming gone bad on this site.
Good luck