Captain America is technically over 100 years old and still looks like he is in his 30s. This is mainly due to the fact that he was frozen for 70 years. When he was revived, he has lost almost all of his family. Peggy Carter is old and in her death bed. Bucky is missing. Captain America eventually finds Bucky alive in events of Captain America Winter Soldier. In Avengers: Endgame, he and the remain avengers had to go back to the past to collect the Infinity Stones to fight Thanos. When he went back to 1970s to collect the Tesseract and Pym particles, he sees agent Peggy Carter. He realized that there is a possibility for him to have the life he always wanted.
Once the world is saved, he had to return the Infinity Stones and the Mjolnir back to their correct time. He decided that instead of coming back, he would stay with Peggy Carter in the year he first disappeared. He lived a happy life and eventually passed his shield to Sam Wilson ask Flacon to take his place. For somebody close to 200 years, he looked really good for his age.