The labor force participation is naturally going to decline over the next couple decades simply due to demographics. There's no point in attempting to fix it to a certain figure.
And why is it going to decline? Please explain.
Because there's a perfectly predictable increase in the number of people over 65 as baby boomers retire and live longer. The population of those 65+ will be a larger share of the population in the next couple decades.
There is nothing set in stone that says a baby boomer will retire at the retirement age.