Ditto on Charles' "fried-calves" comment....I'm 46 as well and started with 60 seconds jumping, 30 rest, 60 on, 30 off for a full 7 minutes of jumping total.
Calves were VERY unhappy with me..
If you can't seem to do it, keep jumping if you miss and just keep plugging away.
Practice jumping without a rope and just move your arms/wrists like they are holding a rope to mimic the move. You'll get it eventually...it will be the best 5 minutes of cardio you can imagine (other than 5 minutes of alternate 1 hand swings with a kettlebell)
Don't give-up on this fantastic move!