i see both root and alastair cook reached their 10,000 test runs 157 days after their 31st birthdays.
cook was a day younger, however, due to the leap years in his first 31 years.
however, root managed it in 9 years and 171 days, whereas cook took 10 years and 87 days. (note: these times are from 1st day of test debut to 1st day of match the 10,000th run came in).
the only other player to to it in less than 12 years was raoul dravid who took 11 years and 280 days, more than two years longer than root. root is the 14th player to reach 10k.
among other notables (and they're all notables really)
lara 13 years 250 days
tendulkar 15 years 121 days
however, lara, tendulkar, and sangakkara took 195 innings and ponting 196.
root took 218 innings and cook 229. only border, chanderpaul, and steve waugh took more innings.
of the 14, only cook (45.35) ended with an average current below root's (49.57). jayawardene (49.84) was the only other one to average below 50. the highest averages were sangakkara (57.40), kallis (55.37), and tendulkar (53.78).
higher averages below the top 14 in the most runs list are sobers (31st most test runs, ave 57.78), steve smith (33rd, 59.77, 8010 runs, still playing). bradman is 55th on the list.