sick runt puppy

I have an 8 year old Pit Bull Terrier (Blue) that I’ve owned for a little over 3 years now. He’s an experience stud and even though I’ve studded him with the help of his previous owner/breeder, I just wasn’t sure that I wanted to go through the task of breeding myself. His last successful mate was about 1 & 1/2 yrs ago. Another attempt was made after that but the female was a bit aggressive and not very receptive. Well, things have changed since then. I got a female who is now 18 months old (Pit Bull Terrier / Blue Brendle) who I know would be perfect for breeding. She’s in her 2nd heat now and I think her and I both are ready to have a go at this. She seems up to it as she’s always wanting him to sniff and flags here and there. IT’S JUST DAY 1 OF BLEEDING and I know they will do their business in due time. I JUST WONDER IF MY “OLD BLUE” IS UP TO IT SINCE HE’S BEEN OUT OF THE GAME FOR OVER A YEAR NOW. He seems disinterested at the moment when during her first heat, I could barely keep him away from her. PLUS LET’S NOT FORGET HE’S 8 YRS OLD. SO, HOW OLD IS TOO OLD FOR A STUD? I’m still in contact with his previous owner/breeder..just wanted other opinions/tips. Anixiously awaiting…Boom’s Blues.