There has to be a balance. It's certainly a good thing to have some older players who are bringing experience to the team, but obviously you don't want too many or you run the risk of a huge drop-off coming soon. A good example for us is when Fergie left. For all the incredible work he did and he will rightfully go down as arguably the greatest manager of all time, he did leave behind a team that was very much on it's last legs. The great defence with Evra, Rio and Vida were all coming to the end, Carrick, Scholes and Giggs in midfield, Rooney (younger but Fergie could see he was reaching the end) and perhaps you can include van Persie up front. There was just too much left to do.
So the key is to get the balance right.
At the moment we have lost the experience of Carrick, Rooney and Zlatan over the last 12 months. Our other older players:
Young - 32 (probably a squad player next season, replaced by younger starter)
Valencia - 32 (probably a squad player next season, replaced by younger starter)
Mata - 30 (squad player)
Fellaini - 30 (looks likely to go, replaced by younger player)
Matic - 29
Sanchez - 29
Smalling - 28
Herrera - 28 (squad player)
Rojo - 28 (squad player if still here, could be replaced by similar aged starter)
Darmian - 28 (almost certainly going)
Blind - 28 (almost certainly going)
Basically, we currently only have two or three of our starting players next season in that kind of age frame. Otherwise we're going back to Jones and Lingard as our next oldest (not counting the keepers). As such we do have the option for another one or two 'older' players to come in and strengthen our starting line-up, although I wouldn't want more than that.