Manchester United  defender Rio Ferdinand  believes Wayne Rooney  has been the club's "best player this season".The England forward has scored seven goals in 15 games for the Red Devils in 2013-14 and the centre-back thinks that he is starting to really shine thanks to regular football as United push on under new manager David Moyes."I just think with Wazza, if he's playing continually - week-in, week-out - with no injuries then you get a fit, striving, thriving Rooney," Ferdinand enthused to the Daily Mirror. "He's been our best player this season. He's scoring goals, he's making goals and he has the bit between his teeth at the minute."He seems like the old Wayne Rooney. He's happy and he's enjoying his football. You can see his tail's up."We have two unbelievable match-winners in him and Robin [van Persie]. We're lucky to have them. When you have two like that who can win you a game by themselves, you just need the other people to play their part and you can be successful."Our season isn't where we want to be yet but we can see there is a path building. There wasn't a problem of belief at the start, there was just a getting-to-know period. I think you need that in any new job [but] we're through that now and the results show you that."The training is a little more intense. That's the way the manager likes it. We've all warmed to that and we enjoy it. We work a bit more on set-pieces, I'd say, but there aren't massive differences." Ferdinand is not sure, however, whether he will be able to play on past this season as he becomes increasingly frustrated by the limitations of his ageing body."The manager just didn't play me [against Arsenal]. I played midweek and then not at the weekend," the 35-year-old added. "It's frustrating but my age doesn't lie."I have to come to terms with the fact that I can't play every game. It's hard to do because you want to play every game every week but you've got to be professional. At a club like United, when you get to 35, you have to share responsibilities."If you want to be successful in a number of competitions you can't just play the same team week-in, week-out. Now it's common for players to come in and out of the team and it seems seamless for the individual."I don't know [if I'll retire]. I've got to get through this season first. I hope I finish this one. Last season I said the same thing. I won't look any further than the end of the season and then re-evaluate it around that time."