It's an odd anachronism that 21 is still considered such an important age.
In Australia, for example, 21st birthdays are widely celebrated much the same as 18th birthdays, even though minors legally become adults once they turn 18. Cards are adorned with keys, cakes are baked in the shape of them, symbolizing the bestowing of the keys of adulthood to people who have been adults for three years.
For whatever reason, turning 21 remains a mystical moment. The coming of age.
If Mitchell Marsh plays in Bengaluru, his Test career will turn 21. But it feels as though he's been coming of age for a very long time.
Consider Marsh when he first hit adulthood. After captaining Australia to victory in the U19s World Cup, he was playing for Deccan Chargers in the IPL as an 18-year-old alongside Adam Gilchrist in a team coached by Darren Lehmann, a fact that seems almost ridiculous in its generational incongruity.
Seven years and 20 Tests down the track, Marsh has a batting average of 22.79 and 29 wickets at an average of 37.27. That he is blessed with an abundance of talent is undeniable; that talent comes with expectations his critics feel have not been met.
Marsh-bashing is a frequent occurrence on social media and the selection of brothers Mitchell or Shaun is guaranteed to spark a new round. The younger brother has the added burden of being an Australian allrounder, a position that attracts more scrutiny and criticism than most.
Just ask Shane Watson.
In fact, Marsh does just that. Heralded as the natural replacement for Watson at the end of his Test career, Marsh now seeks him out for advice.
"I've spoken to Watto," Marsh said. "Since he's retired he's been fantastic. He's always been open to me giving him a call or a text. I could use him a little bit more, he's always open for a conversation which is great."
Watson could no doubt give just as much advice on how to cope with flak off the field as he could on how to perform on it. When he passed the allrounder's mantle on to Marsh it came with a target attached, something that unsettled Marsh to the extent he stopped reading comments about himself on social media altogether.
"I try not to look too much into it," said Marsh. "I wouldn't have too much confidence if I read all the comments on Facebook. That's part and parcel of playing cricket for Australia at the top level. People are always entitled to their opinion, that's fine by me. It doesn't stress me out. I used to read a lot of it then I had 10 innings where I didn't get over 30, I didn't have much to read so I stopped reading it.
When the selectors cut a swathe through the Australian squad in the wake of the humiliating loss to South Africa in Hobart they didn't miss Marsh. He had played only the Perth Test and was left out of the Hobart match in favour of Callum Ferguson. With no opportunities available to play first-class cricket, he returned home to join up with the Perth Scorchers.
"In a way it was probably a good thing because I just went back to the Big Bash and enjoyed myself, tried to slog a few and managed to get a few out of the middle," said Marsh. "But away from the game I worked on a few things that I feel will hold me in good stead if I can play in Australia again or play in other conditions. Sometimes it's nice to get out of the spotlight. I was obviously under a lot of pressure for a while so in a way it was nice to get back to play with the Scorchers and here I am."
Marsh wasn't required for bowling duties in the first Test but he applied himself for a watchful 31 runs on the crumbling pitch. For a powerful, attacking batsman, it was a commendable show of restraint in such conditions. It was followed by dressing-room celebrations that Marsh described as the best four hours of his life.
"It was good, it gave me a lot of confidence," said Marsh. "Even though I made only 30, being out in the middle for 80 balls certainly gave me a lot of confidence. Hopefully this wicket is a little better and I can turn it into a big score for us."
"I think it's just about adapting. That's something we always speak about, Steven (Smith) always talks to us about it. In these conditions you've got to earn the right to attack and that's by having a solid defence. That's what I've been working on."
Marsh has also been working on gaining the trust of his brother. Shaun's nine-month old son, Austin, is on the tour and Uncle Mitch is being allowed to babysit his nephew for the first time.
"You earn your trust," said Marsh, while conceding he wasn't very confident on nappy-changing.
"It's taken me a while but I've got there now."
If he can produce his best in India, that's a statement he may make for many Tests beyond his 21st.