First allow me to apologise for this seemingly elementary question. I am a complete novice to Stata and other answers in the forum weren't too helpful for me.

I have merged the LEAD and Archigos leaders dataset with the Maddison GDP data (not shown here).

idacr gdpyear leaderid leader outyear age careerpolitician
"" 1919 "LEAD.v1-1114" "Barquero" "1920" "63" "1"
"AFG" 1820 "NA" "NA" "NA" "NA" "NA"
"AFG" 1868 "LEAD.v1-7693" "Shir `Ali Khan" "1879" "54" "0"
"AFG" 1870 "NA" "NA" "NA" "NA" "NA"
"AFG" 1879 "LEAD.v1-7696" "Mohammad Ya`qub Khan" "1879" "30" "1"
"AFG" 1879 "LEAD.v1-7699" "Mohammad Jan" "1880" "NA" "0"
"AFG" 1880 "LEAD.v1-7702" "Abdor Rahman Khan" "1901" "57" "0"
"AFG" 1901 "LEAD.v1-7705" "Habibullah Khan" "1919" "47" "1"
"AFG" 1913 "NA" "NA" "NA" "NA" "NA"
"AFG" 1920 "LEAD.v1-7708" "Amanullah Khan" "1929" "37" "1"
"AFG" 1929 "LEAD.v1-7711" "Inayatullah Khan" "1929" "41" "0"
"AFG" 1929 "LEAD.v1-7714" "Habibullah Ghazi" "1929" "39" "0"
"AFG" 1929 "LEAD.v1-7717" "Nadir Shah" "1933" "53" "0"
"AFG" 1933 "LEAD.v1-7720" "Hashim Khan" "1946" "62" "1"
"AFG" 1946 "LEAD.v1-7723" "Mahmud Khan Ghazi" "1953" "65" "1"
"AFG" 1950 "NA" "NA" "NA" "NA" "NA"
"AFG" 1951 "NA" "NA" "NA" "NA" "NA"
"AFG" 1952 "NA" "NA" "NA" "NA" "NA"
"AFG" 1953 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "54" "1"
"AFG" 1954 "NA" "NA" "NA" "NA" "NA"
"AFG" 1955 "NA" "NA" "NA" "NA" "NA"
"AFG" 1956 "NA" "NA" "NA" "NA" "NA"
"AFG" 1957 "NA" "NA" "NA" "NA" "NA"
"AFG" 1958 "NA" "NA" "NA" "NA" "NA"
"AFG" 1959 "NA" "NA" "NA" "NA" "NA"
"AFG" 1960 "NA" "NA" "NA" "NA" "NA"
"AFG" 1961 "NA" "NA" "NA" "NA" "NA"
"AFG" 1962 "NA" "NA" "NA" "NA" "NA"
"AFG" 1963 "LEAD.v1-7729" "Mohammad Yusuf" "1965" "48" "1"
"AFG" 1964 "NA" "NA" "NA" "NA" "NA"
"AFG" 1965 "LEAD.v1-7732" "Mohammad Hashim Maiwandwal" "1967" "48" "1"
"AFG" 1966 "NA" "NA" "NA" "NA" "NA"
"AFG" 1967 "LEAD.v1-7735" "Abdallah Yakta" "1967" "NA" "0"
"AFG" 1967 "LEAD.v1-7738" "Nur Ahmad Etemadi" "1971" "50" "1"
"AFG" 1968 "NA" "NA" "NA" "NA" "NA"
"AFG" 1969 "NA" "NA" "NA" "NA" "NA"
"AFG" 1970 "NA" "NA" "NA" "NA" "NA"
"AFG" 1971 "LEAD.v1-7741" "Abdul Zahir" "1972" "62" "0"
"AFG" 1972 "LEAD.v1-7744" "Mohammad Musa Shafiq" "1973" "41" "0"
"AFG" 1973 "LEAD.v1-7747" "Sardar Mohammad Daud Khan" "1978" "69" "1"
"AFG" 1974 "NA" "NA" "NA" "NA" "NA"
"AFG" 1975 "NA" "NA" "NA" "NA" "NA"
"AFG" 1976 "NA" "NA" "NA" "NA" "NA"
"AFG" 1977 "NA" "NA" "NA" "NA" "NA"
"AFG" 1978 "LEAD.v1-7750" "Taraki" "1979" "62" "1"
"AFG" 1979 "LEAD.v1-7753" "Amin" "1979" "50" "1"
"AFG" 1979 "LEAD.v1-7756" "Karmal" "1986" "57" "1"
"AFG" 1980 "NA" "NA" "NA" "NA" "NA"
"AFG" 1981 "NA" "NA" "NA" "NA" "NA"
"AFG" 1982 "NA" "NA" "NA" "NA" "NA"
"AFG" 1983 "NA" "NA" "NA" "NA" "NA"
"AFG" 1984 "NA" "NA" "NA" "NA" "NA"
"AFG" 1985 "NA" "NA" "NA" "NA" "NA"
"AFG" 1986 "LEAD.v1-7759" "Najibullah" "1992" "45" "1"
"AFG" 1987 "NA" "NA" "NA" "NA" "NA"
"AFG" 1988 "NA" "NA" "NA" "NA" "NA"
"AFG" 1989 "NA" "NA" "NA" "NA" "NA"
"AFG" 1990 "NA" "NA" "NA" "NA" "NA"
"AFG" 1991 "NA" "NA" "NA" "NA" "NA"
"AFG" 1992 "LEAD.v1-7765" "Burhanuddin Rabbani" "1996" "57" "0"
"AFG" 1992 "LEAD.v1-7762" "Mojadidi" "1992" "66" "0"
"AFG" 1993 "NA" "NA" "NA" "NA" "NA"

I would like to know how I can replace the missing values with the values in the previous row if 'outyear' in the previous row is less than or equal to 'gdpyear', i.e. fill the missing values with data on the same leader until he went out of office. I would also like to know if there is a clever way to replace the missing values for age, which must correspond to a specific leader and not just '+1 from the previous row'.

So the outcome would be something like:

idacr gdpyear leaderid leader outyear age careerpolitician
"AFG" 1953 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "54" "1"
"AFG" 1954 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "55" "1"
"AFG" 1955 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "56" "1"
"AFG" 1956 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "57" "1"
"AFG" 1957 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "58" "1"
"AFG" 1958 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "59" "1"
"AFG" 1959 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "60" "1"
"AFG" 1960 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "61" "1"
"AFG" 1961 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "62" "1"
"AFG" 1962 "LEAD.v1-7726" "Sardar Mohammad Daud Khan" "1963" "63" "1"
"AFG" 1963 "LEAD.v1-7729" "Mohammad Yusuf" "1965" "48" "1"

Thank you.