Is Sans older than Papyrus?

After seeing a True Pacifist Playthrough (did not see any other routes) I checked out the Undertale wikia. During the playthrough I noticed Sans and Papyrus talking about who's older. If I recall this correctly, there was something along the lines of 'Papyrus, but Sans reads night stories for him therefore Sans could be his older brother'. I don't know whether there were any other hints.

I looked at the Undertale wikia page for Sans and found that Papyrus is a younger brother to him. (Link)

Is there any other information that hints at who is the older brother?

Solution 1:

There's no definitive in-game/canonical evidence as to which brother is older.

It's obvious that they both care about each other, however the Wiki entries for Sans and Papyrus just list them as 'brothers', and everything in-game pointing one of them being the older sibling is circumstantial at best - most likely played this way so as to leave it up to the player's own interpretation/head-canon.

Some parts of the story points to Sans being younger:

• Papyrus encourages & cajoles Sans for his laziness:

  IT'S BEEN EIGHT DAYS AND YOU STILL HAVEN'T... RECALIBRATED. YOUR. PUZZLES! ... YOU GET LAZIER AND LAZIER EVERY DAY!!!
  _{- Papyrus}

• Sans admires his brother

  my brother's a real star....

• Who encouraged him to take a job as a sentry:

  ...he's the person who pushed me to get this sentry job.
  _{- Sans}

Other pieces of the story point to Sans being older:

• Sans has a 'real' job & takes care of his brother/pays the bills
• Sans reads Papyrus bedtime stories and gives him presents

  Sans cares for and admires his brother. He reads him bedtime stories and gives him presents under the identity of Santa.
  _{- Undertale Wiki}

There are some other fan-theories & explanations out there, for example, that they are as old as the creation dates of the fonts the characters are based on: Comic Sans and Papyrus, but again, as these are just fan-theories and aren't confirmed in-game in any way.

Finally, it's worth mentioning that the developer of the game - Toby Fox - has also previously tweeted that Papyrus might use the Japanese word 'Aniki' (i.e. 'Older Brother' or 'Superior' in Japanese):

Papyrus would definitely use "aniki." i think. what's your take.
_{- Toby Fox. September 10, 2015 (Internet Archive)}

Again, this isn't covered in-game and Toby has since deleted this statement. Thus it shouldn't be interpreted as 'Word of God' (TV Tropes). Even if the statement hadn't been recanted, there is still enough evidence to point either way in game, thus it would still be open to interpretation.

Until (and if) we get another source of official canon material (such as a second game, comic, movie etc) that builds upon or embellishes the story, we don't have the evidence to say which brother is older than the other. It's ultimately up to you to decide.

Solution 2:

In Korean, there are different words for older and younger brothers. In the Korean version, they use the word 동생 when talking about Papyrus, which means younger brother, so it's implied that Sans is the older brother.