At the end of the day the PPL still has to meet the FI standard which I have a good understanding of as I am qualified to teach for the instructor rating in Canada. My experience doing many PPL annual proficency check rides at my flying club is that pretty much all of the PPL's would require quite a bit of remedial instruction on the stick and rudder basics before I could actually start the FI course. I also found in general the higher time pilots who had held a PPL for several years had the weakest handling skills. Nevertheless I would much rather work with someone who has a genuine desire to teach instead of someone who is using the FI as necessary evil to endure on the way to the airline job. Also the life and people skills age brings, can be very effective in the context of teaching the range of personalities you get at the club level.