I am just getting over a knee replacement...football ahhh anyway I'm 60 now and try to keep in shape. i really need some feedback on weight training reps vs weight...I'm told 40 pounds is max weight to lift...so will just reps build up my legs?...any experience out there as I can't get a good answer...suggestions

the key I suspect is your knee, what does the specialist say? 
At 65, male, weighing 83k I use weights regularly just as a keep fit.  I do nothing special for weights and tend to keep things fairly low key.  I am currently doing one set of 5 reps using a free weights bar with each exercise plus various core exercises:
Bent over rowing 53k, military press 36k, squat jump (train on my own so the lower weight of the squat with a jump is safer) 43K, dead lift 86k.  Sometimes I do a straight leg dead lift instead. 
Aim is weights once per week and sometimes do twice.
In addition general flexibility movements including full knees bends,  chins 4 or 5 and 10 press ups several times per week.
I cycle, kayak regularly with occasional other sports.  Having a heart arrhythmia significantly effects what I can do.
During the winter I will raise the weights to sets of 10 at lower weights, perhaps 2 sets twice per week.  I will change the exercises sometimes but try to keep to 4 covering the major movements.
Is this the sort of info you needed?
But the key is start low and progress slowly.  So if you start with no weight for an exercise and build slowly so for example even at 1kg per week increase you would reach my 86k dead lift in under 2 years.  Sounds a long time but it isn't really and would keep you safe.  Dr Mirkin has a good piece on starting a weight programme.