The article is 20 years old, so the data is not very recent.
Yet, it provides the following age data:
"Death row inmates in 2000 ranged in age from 18 to 85 years old, with a median age range of 35 to 39 years (19.1% of the total sample)...Median age at time of capital arrest was 27 years—with 40% age 24 or younger, 10.7% age 18–19, and 2.4% age 17 or younger...
These women range in age from 21 to 71 with a median (40%) age range of 30–39. Their tenures on death row range from less than a year to over 19 years...
With these caveats noted, Strieb (2001b) reported that 200 juvenile offenders, including four females, have been sentenced to death since 1973—representing less than 3% of all age offenders receiving death sentences. Half of these death sentences have been handed down in three states: Texas (50), Florida (30), and Alabama (21). Approximately 70% of juvenile offender death sentences were imposed on individuals who were 17 at the time of the capital offense. Seventeen (8%) have subsequently been executed, while 110 (54%) had their death sentences reversed. Of the 17 juvenile offenders executed, all were males and all but one had been 17 at the time of the capital offense.
Seventy-five (37%) of the 200 juvenile offenders sentenced to death remain on death row. All are males. Twenty-six (35%) are on death row in Texas. Offenders of racial minority origin are more heavily represented on death row among juvenile offenders than adult offenders (66% versus 54%). Tenure among juvenile offenders on death row ranges from less than one year to over 22 years, and their current age range is 18–42 years (Strieb, 2001b). Eighty percent of the 101 victims of these juvenile offenders were adults, two-thirds were white, and half were females (Death Penalty Information Center, 2001)."
Age and the effect of death penalty has no significant correlation With age maturity sets in and I have noticed in my Criminal Propensity Scale that Psychoticism and Neuroticism declines The offender is less violent and accepts the idea of rehabilitation
Besides generally considering the age death penalty as per the UNStandard Minimum Rules is converted to life imprisonment except in very rare case
I couldn’t find any studies related to this particular question.
Still, I found a literature review, "Death Row Inmate Characteristics, Adjustment, and Confinement: A Critical Review of the Literature" - https://files.deathpenaltyinfo.org/legacy/documents/CunninghamDeathRowReview.pdf
The article is 20 years old, so the data is not very recent.
Yet, it provides the following age data:
"Death row inmates in 2000 ranged in age from 18 to 85 years old, with a median age range of 35 to 39 years (19.1% of the total sample)...Median age at time of capital arrest was 27 years—with 40% age 24 or younger, 10.7% age 18–19, and 2.4% age 17 or younger...
These women range in age from 21 to 71 with a median (40%) age range of 30–39. Their tenures on death row range from less than a year to over 19 years...
With these caveats noted, Strieb (2001b) reported that 200 juvenile offenders, including four females, have been sentenced to death since 1973—representing less than 3% of all age offenders receiving death sentences. Half of these death sentences have been handed down in three states: Texas (50), Florida (30), and Alabama (21). Approximately 70% of juvenile offender death sentences were imposed on individuals who were 17 at the time of the capital offense. Seventeen (8%) have subsequently been executed, while 110 (54%) had their death sentences reversed. Of the 17 juvenile offenders executed, all were males and all but one had been 17 at the time of the capital offense.
Seventy-five (37%) of the 200 juvenile offenders sentenced to death remain on death row. All are males. Twenty-six (35%) are on death row in Texas. Offenders of racial minority origin are more heavily represented on death row among juvenile offenders than adult offenders (66% versus 54%). Tenure among juvenile offenders on death row ranges from less than one year to over 22 years, and their current age range is 18–42 years (Strieb, 2001b). Eighty percent of the 101 victims of these juvenile offenders were adults, two-thirds were white, and half were females (Death Penalty Information Center, 2001)."
And here is another article I found you might find interesting - “Death Row Phenomenon. A Fate Worse Than Death. Torture on death row from a psychological and legal perspective.” - https://repository.gchumanrights.org/bitstream/handle/20.500.11825/174/Hempel.pdf?sequence=1&isAllowed=y
Age and the effect of death penalty has no significant correlation With age maturity sets in and I have noticed in my Criminal Propensity Scale that Psychoticism and Neuroticism declines The offender is less violent and accepts the idea of rehabilitation
Besides generally considering the age death penalty as per the UNStandard Minimum Rules is converted to life imprisonment except in very rare case