Are Roth conversions done prior / before age 59 1/2 subject to the 10% IRS penalty on the taxes paid on the conversion amount . ?

Yes. Taxes on conversions are intended to be paid from outside funds. If under age 59.5 and you use any of the converted funds to pay the tax it's subject to the 10% penalty ... took and early distribution to pay the tax.

But see if taxes are paid outside Roth IRA
See below from final Roth Regs 1.408A-4

Q-7. What are the tax consequences when an amount is converted to a Roth IRA?





A-7. (a) Any amount that is converted to a Roth IRA is includible in gross income as a distribution according to the rules of section 408(d)(1) and (2) for the taxable year in which the amount is distributed or transferred from the traditional IRA. Thus, any portion of the distribution or transfer that is treated as a return of basis under section 408(d)(1) and (2) is not includible in gross income as a result of the conversion.




(b) The 10-percent additional tax under section 72(t) generally does not apply to the taxable conversion amount. But see §1.408A-6 A-5 for circumstances under which the taxable conversion amount would be subject to the additional tax under section 72(t).




(c) Pursuant to section 408A(e), a conversion is not treated as a rollover for purposes of the one-rollover-per-year rule of section 408(d)(3)(B).