At what age do you consider a male puppy sexually mature? I'm not talking about the age he should be first bred, I'm referring to the age at which a male Lab pup is capable of impregnating a female.
TIA.

At 7 month it should be capable to produce puppies. 10 month for better chances and, I think, 2 years for complete development and pick of semen quality.

6-7 months - be careful!

Depends on the breed & history- smaller the breed the earlier. Giant breed can be well over 1 year. Labs 7-9 months I lean more toward 9 months capable but not likely. Better yet many don't seem to get it naturally. Collect some and they won't finish naturally themselves- they look for the hand.

I had a surprise litter of two sired by a 7 month old about 20 years ago. The female was on day 23 and no longer standing, and I only left them for about 30 seconds. How he got the tie I'll never know. She HATED him for at least 6 months, so I don't think it was her idea. Be careful is right!

"She HATED him for at least 6 months"

Well lets see...depends on what they have been watching on TV.. where they sleep and what they see________________ you fill in the blanks. Yep, 7 months they can "party"...then they probably figure they can lift their leg. Nothing is more priceless then the look on a male labs face the first time he has a natural tie, looks back to the business end and gives it a double take as he thinks it's gone.