From 2002-2012

16-55 made up 22.1% of population growth, however accounted for -15.3% of labor force growth.
The 55+ age group has made up 77.9% of population growth, however accounted for 115% of labor force growth.

Meaning...The 16-55 age group as a percentage of the labor force is growing less than the 55+ age group. Easily the 55+ age group is making up most of growth in the labor workforce.

16-55 age group 722,000 not entering/leaving labor force per year. (population grew 5.7m, labor force grew negative! (-1.5m!)
55+ age group 838,000 leaving labor force per year. (population grew 20.1m, labor force grew +11.6m )

The total population growth of these two groups.
16-55 +5678 (22.1%)
55+ +20036 (77.9%)

Those 55+ are entering the workforce at a rate of about 58.2%
The 16-55 are entering the workforce at a rate of -27.3% (negative number)

Obviously the 16-55 age group is dragging down the LPR far more than the 55+.

The claim LFPR is reduced due to retiring citizens is a falsehood.