When I had my other two dogs (both sadly now passed away) I waited till my Lab bitch was a year old and then got an 8 week old Goldie male puppy.  It worked out very well , although maybe I was just lucky!

I now have a 15 week old Goldie boy and would love to  have two again.  Just wondering in other members experience what is the best age for my boy to be before getting a new puppy? And what sex would be best?

I should wait until your pup has grown up and matured before getting another, somewhere round about when he is two years old. I got another goldie when the older one was about 13 months and really it was too soon and it was nearly like having two puppies at the same time. The older one did teach the younger one quickly about the need to go outside to toilet, but then also passed on all her naughtiness onto the youngster, consequently they formed a mini pack and gave us the runaround.
My current goldie is three now and a calm well behaved dog and I wouldn't mind a second one now if we were going to have two dogs.

We waited till our girl was two and a half before we added another pup, and the youngster was eighteen months when when we took on our secondhand boy. They all get on really well and we have not had any issues so far. All are Golden Retrievers.

I've waited before now and had just under an 18 month gap, same sex and breed and never again. You want your existing dog to be well mannered and trained before bringing in another, unless you have the time to keep them apart and train them daily apart from each other and walk them apart I wouldn't be doing it. Until your pup now is mature and you can see how he behaves I wouldn't be thinking of another just yet.
My current age split is 4yrs between the eldest two and just over 4 years between the middle and the youngest who is 10 months. I would consider another but not until the youngest is at least 18 months and I would go for the opposite sex to her at that age gap

Another here who strongly recommends an age gap of at least 2 years or preferably more.
My youngest are now 3.5 & the next is 10 years, ok the next is 11.5  but the next is 14 next week.
Personally I think a good age spread helps for a number of reasons, some have already been mentioned but one which hasn't, is your less likely to loose loved ones too close to each other. 

I also recommend 18 months to 2 years between dogs at least.  (I'm a trainer and behaviourist.)

Personally, I prefer much longer between my own dogs so I have time to focus on just one 'career' at a time - ideally one is 5yo at least, before I add a pup.

Guess I just got lucky last time, and you are absolutely right Lexy, losing both within five months was just heartbreaking.
thanks to everyone for the input

I'm another to suggest leave it until your current one is approaching 1 year although IF you have experience and realise what having two puppies at the same time really means it may be okay.   In which case although I'd not do this right now, you might look at getting a second between 6 and 12 months later.   A female.   Obviously she'll have to be spayed, and in that, it might have been better to get a female first, spayed when the right time, and then think about a second - a male.

It is possible for two males to get along of course, but the ideal combination is one of each.   I understand your feeling about wanting two again however!

ps    We have always kept back at least 2 puppies from our litters, which can mean losing two at around the same time.   We had 3 from one really good litter, lost both girls in short order and then their brother - I always felt he'd hung in there to allow us to get over losing his sisters..... probably not but.....?    With the final two of our bloodline, yes, brother and sister, we lost the sister first after fighting cancer for her over a year, and then in short order, her brother developed oral cancer.   She was in her 12th year and he, his 13th.  So quite quickly we'd lost all our bloodline.    Heartbreaking.   But we had bought another breed before we lost the male, so there was always one in the house.   Still hard after having up to a dozen around at one stage.

Another person saying wait, enjoy the puppy and adolescent stages before doing it all over again!

I agree that you need to wait at least 2 years.  Once the current pup has had all his training and behaves less like a hooligan!

Another one recommending you wait :-)

Three years but at least two. I hat two pairs that are 15 months and 19 months apart respectively,  and thankfully 2 1/2 years between the two pairs.  I have found it much harder with uh shorter age gaps,  but my breed are very much pups until two,  so really need that extra time to get them to the stage you want before being able to concentrate on a new pup.