$4,000 "age tax"?

Average premiums would increase for all ages starting at about age 46.
Premiums for 60- to 64-year-olds would increase by an average of $3,200, amounting to average unsubsidized premiums of almost $18,000 per year. Meanwhile, 20- to 29-year-olds are expected to see significantly smaller average savings, of only $700 per year, giving them average unsubsidized premiums of $4,010 per year.

https://www.aarp.org/politics-society/advocacy/info-2017/older-adults-pay-more-with-age-tax-fd.html

with his plan to make permanent the current "holiday" from paying the FICA tax.

Most people don't realize that Social Security is a pay-go situation, where the current benefits are paid by the currently collected FICA tax, plus a small amount from the SS Trust Fund. Thanks to Reagan, the FICA tax was made part of the General Operating Fund, leaving the SS Trust Fund to not grow. We have the current benefits being paid out of the Operating Fund - IOW, the Operating Fund is enlarged by the FICA tax - and a small amount being drawn from the SS Trust Fund, which is not being replenished. If Trump makes the current holiday from paying FICA permanent, that is, in effect, reducing employer's taxes by the ~7% that they match for SS and Medicare and reducing the General Operating Fund. The SS Trust Fund, being the only thing left to pay benefits at that point, will run dry in 2023 (estimates by SS Administration) and SS Disability payments, which come out of only FICA, will dry up in 2021; probably the same for Medicare, although no statement has been made about that.


Social Security could come to a screeching halt:
https://www.cnn.com/2020/09/01/opinions/social-security-payroll-trump-altman/index.html