I don't think you are a coward by any means, You are just starting to realise you are no longer a 18 year old invincible person, in fact you are lucky to be having self doubt now rather than as some of us finding out the hard way that we no longer have the agility or the super fast reflexes we once had.
I still cruise at around the 120km mark unless I feel it is either safe to go up to say 130 or 140 but this is only after assessing the risks eg visibility road conditions etc, also the other risk of being booked comes into play, just the other week while cruising along at 130kph coming home from Phillip Island along a stretch of back road in good condition and towing my camper a car flashed his lights at me as we do to warn of speed traps so I immediately rolled of the throttle and as I got closer I realised it was in fact a unmarked highway police car! And he just waved. The curious thing is this was on Victoria said by some to be full of cops that are hard on bikes another interesting thing is that later the same day it happened again twice but the fact I corrected my speed in each occasion is what I think got me home with out a ticket.
I ride by my gut feeling if I feel it is safe to go harder I do but always access the Risk and that includes if you feel a little off then don't go for a ride simple as that!
No You are not a Coward Just realising your Limitations