My puppy was 20 weeks old yesterday (Dog).My other dog (Bitch) started her season yesterday about 2 months late.I had it all worked out that she would be speyed well before he was interested in her  you know best laid plans and all that.I'm not sure whether he could successfully mate with her at this age, I'd like some guidance on this point please. The breeder has told me he's ok until he's 6 months old but I'd like some other opinions please as I don't want any unwanted pups. Obviously I have separated them, how does everyone manage when it comes to walks and car journeys?
ange

Had a dog enter a bitch at 15 weeks, don't know if it would have produced any results and I was in the room and intervened. May be it is different with different breeds.

Jackie's answered your first question - yes, he's probably physically capable of mating, so keep them entirely separate.

For walks and car journeys? Take them separately. It would be best if one could stay with a trusted friend or relative until your bitch's season is well and truly over.

At the end of the day its just not worth the risk!
Archer