The rate of employed in the age 55-64 is really to low in France (in 2005, 37,9 % against 44,1% in the EU-15, 56,9 % in the UK). it is not sustainable with the highest life expectancy in Europe (78 y)
So if you take out the few % where work is indeed physically demanding, you can without any problem get higher than our current level.

Concerning young people, I don't see the point of luring people in thinking they will have jobs when their specialization wil not provide them to them. I am an advocate for more money for less people in universities

You're right that UK's model is to put low qualified people on part time jobs, while in france they don't get any. I'm not sure this is wrong, even if, i agree, it nuances the figures i put forward

Regarding the disclaimer about non comparability, i did not see something as precise as you say. However, i tend to believe that the difference still remains (it is 149 hours / year, or more than 3 hours/week. i don't see every worker in france doing so much extra work hour)