The Brazilian has been one of United's most consistent performers this term and will look to help maintain his side's six-point lead at the top of the Premier League when they host Sunderland on Saturday.
The 22-year-old has also played more games - 21 in all competitions - than any other player in United's squad this season and thinks Fabio's loan move to QPR has helped him develop.
Asked what was behind his form, Rafael said on Manchester United's official website: "I think this is just a natural development, it's bound to happen when you play more games and have more experiences.
"My daughter has also helped me, [being a father] has settled me down a lot. When you're a dad you have to be mature.
"Also, I think splitting from Fabio has been a good experience. At first I was sad, but I've come to see that it's made me grow up a lot. I've had to change and be more responsible."
Manchester City will look to keep the heat on the leaders by bouncing back from last weekend's last-gasp derby defeat when they travel to Newcastle in the early kick-off.
Roberto Mancini's men fought back from 2-0 down to draw level at 2-2 with their bitter rivals, only to concede a Robin van Persie goal in stoppage time.
But captain Vincent Kompany claimed that loss has not dealt the squad a psychological blow.
"I don't know anything about psychological blows," he said. "Losing on Sunday changes nothing. We lost and we move on to the next game.
"The beauty of football is that you are always challenged, whether you have lost or won, and the next game is always the most important.
"We all know the importance of the (Newcastle) game but I don't do very well in bad-scenario thinking.
"For me there are so many positives that can happen if we win that game - I can't think of the other side of that coin."
Newcastle are equally in need of a win, having lost four of their last five in the league and sitting just two points above the drop zone.
Bottom side QPR have the chance to finally claim a first league win of the campaign, at the 17th attempt, when they host west London rivals Fulham.
Rangers have amassed just seven points from 16 games, but at least are unbeaten in three since Harry Redknapp took charge.
And midfielder Stephane Mbia is convinced the club can escape from trouble.
He told the club website: "Nobody expected us to be in the position we are in, but I believe the fans know we are good enough to come out of this.
"I am sure, very convinced, we will get out of it. It is up to the players to make this happen."
On Monday, under-fire Arsene Wenger will demand a response from his Arsenal side as they aim to bounce back from their humiliating penalty shoot-out defeat to npower League Two outfit Bradford in the Capital One Cup with victory at struggling Reading.
On Saturday, Everton look to maintain their place in the top four with a win at Stoke, who are unbeaten in their last six games.
Liverpool go in search of a third straight league win when they entertain Aston Villa, while Norwich, who have not tasted defeat in the league since October 6, face Wigan at Carrow Road.
On Sunday, Tottenham host Swansea and West Brom welcome West Ham.