Personally, I don't worry too much. I wouldn't take them on long hikes as such but I certainly don't believe in this 5 mins per month of age rubbish. I think pups who's exercise is TOO overly restricted is more likely to suffer problems when older than those where it's more relaxed. I don't really worry about how long other people walk their pups so long as they bother to take them anywhere at all....no point having a dog and never taking it for a walk.
When I was a child, our pups went on the same walk as our adults after their jabs and we never knew any different. We had a lot of dogs and I can safely say none developed problems from it at all.
Sleet was nearly 16 weeks before she could go out because she was already 12.5 weeks when we got her but Wren could go out at 11.5 weeks or there abouts. They know how much they could do and I didn't see the difference between walking round a field or running up and down the garden or round the house until they dropped to be honest. I used to put them to bed and, as poor Sleet tried to settle down, Wren was wreaking havoc in their little bedroom...I sneakily watched through the window one time and just saw this brown furball bouncing about all over like a powerball having loads of fun...poor sleet who was curled up trying to sleep and getting bounced on. The dog beds were always pushed down against the door next morning and the bedding everywhere. She was such a bugger:D
As for Sleet, she was a real fan of just running running running. I could walk for 15 minutes and she'd cover 5 miles in that time, haha. I didn't stop her because she enjoyed it and I'd have to put her on lead to stop her anyway. One time, I sat down at the top of the hill and she just raced up and down the hill over and over....thoroughly enjoying herself. She stopped when she was ready.
I don't think there's anything wrong with what you're already doing. All pups are different anyway. Like yours, mine just loved to be on the move and they'd do it at home or out on walks regardless anyway and not suffered in anyway as a result of it.
As you can see, Wren was quite the acrobat even as a fluffster...she couldn't half shift. She was 11.5 weeks old here on her first walk with Sleet. She'd been on a few walks in the streets with just me beforehand.
She could scale 5 ft gates and alsorts from when we first got her at 8 weeks...our backs ended looking like Fort Knox because of her.
Sleet was always very respectful of boundaries despite physically being able to get over them easily.