is ther any implications to taking on an older pup he is 16 wks,i already have a dog of 18mnths

I'm no expert, but having just taken on a 6 month old pup (and I have an dog aged almost 3) I would say the only downside is that I have missed out on socialising time, and it is taking longer to get him used to different things. However I have found some good things too eg easy housetraining, also can take him anywhere straight away as he is fully vaccinated, and because he is bigger and more robust he can play well straight away with my other dog. (luckily they get on like they have been best mates for ever!)

It depends entirely on what has been done with the pup. A pup aged 16 weeks needs to have been socialised, started training etc, as you will otherwise have lost several very important weeks (in fact the MOST important weeks). A couple of years ago I had a pup that I didn't find a home for until he was 14 weeks, and so I lead trained him, started teaching basic commands, started house training, and took him out and about to meet people, dogs, see different things, and to training classes etc.

I have a Friend who due to timewasters still has a pup of this age unhomed.

What matters is what socialisation the pup has had.

My friends pup is now lead trained has been leading a full family life, been to lots of places and short and long trips by car.  Is socialised with dogs obviously, chickens, children of all ages.

When he finally goes to his new home they will have had a great head start, housetraining is likely to be a doddle as he already is at the breeders.

On the other hand if the pup has been isolated and in a less knowledgeable environment then you would be starting with a handicap playing catch up.  Depending on the breed and character this may have implications or not.

Depends on the breed also

I got my youngest working cocker at six months old, he came from a gundog trainer/breeder and had been kenneled up until then with 65 other dogs although he was born in a house and spent his first few weeks indoors. He had been taken out to various game fairs etc. where this trainer often does the gundog displays so he'd met plenty of people and seen lots of crowds and hustle and bustle and had been lead trained (although no other training). I met him several times before I bought him and could assess his temperament and trainability pretty well as he was a bit older and he really is the most perfect little dog in pretty much every way. He has taken to his training like a duck to water and is easily the most biddable of all my dogs and in future I'd prefer to get them at this age as long as the socialisation etc. had been done as you can more accurately assess their potential as a working dog at this age plus I don't particularly enjoy the very young puppy chewing/biting/peeing/pooping stage and he was well past all of that!!