United must now pick themselves up following a season that will best be remembered for finishing runners-up to a dominant Manchester City side in the Premier League, with a 19-point gap to be made up next term.
Speaking to reporters after his side's loss to Chelsea, Young said: "I think we have to come back stronger - stronger in the league, stronger in the FA Cup, stronger in the League Cup, stronger in the Champions League.
"We want to be fighting on all fronts. We have the summer now to look forward to and then come back and prepare in pre-season. We wanted to win things, win titles, but it wasn't meant to be. We finished second with the points we did and, in a different season, we would have won the league.
"But it wasn't meant to be and today is a disappointing one. It will take a while to settle in and we now have the summer to prepare for next season."
United boss Mourinho had won all six domestic finals that he had contested in English football prior to this weekend.