If he's not getting into stuff then I wouldn't put him back on the lead. My dogs and cats are the same way as yours. I would still have mine on a lead at 17 months if that was the case. Just keep an eye on him, correct him when you see or hear him doing something he isn't suppose to.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD