That doesnt mean you cant carry your pup for part of the walk. 20 mins on the ground and then a rest and maybe 10 mins at the very end shouldnt be a problem. Carrying them does wonders for your arm muscles

Also bare in mind that you can be out for longer than that providing your pup rests. Ive taken to stopping half way round and leading my pup and getting her to settle down with a chew toy while i do retevial training with my oldest dog. She not damamging her joints but is shattered by the time I get home as shes had the mental stimulation of watching the world go by.
It does take alot of forward planning with 2 dogs of different ages but a bit of thought and its not too disruptive.