Mine are 4.8m x 1.2m and getting to the middle is ok from the paths though more complicated when plants are in. I'm 5ft9 with long arms and demolished some beans by overbalancing last year...
I'm replacing grass path with woodchip this year - grass paths are pretty but they take mowing, get weed-infested quickly - at least mine do, and are v squelchy at this time of year..Path width varies at the moment hopefully will be toe-to-knee by the end of the season, plus wheelbarrow width down the middle
PS my knees are shot too!