Good news. He's one of my favorite United players, a great servant of the club and i believe he deserves to retire on a high note, another PL title possibly.
I don't believe age plays any particular role in a Mourinho side. If you are good enough, then you're old enough. The only question is if he will be able to stay fit for the most part of the season. Plus Mourinho always likes to have experienced players who are a good influence for the others in the dressing room.
I don't think he'll be a first choice for the starting xi next season and that we'll sign a new holding midfielder. In any case, even at 35, he's still a quality option to have in the squad, either as a stopgap during an injury crisis or as a sub who'll help the team control the tempo and see out games.