Despite his club's struggles this season, the 36-year-old is United's top scorer with 14 goals in all competitions.
When asked whether he can see a limit to his longevity, he told ESPN: "I feel happy to be a player who has shown who, in my case, longevity has been a crucial factor for me to keep playing at a high level, putting in good performances.
"Genetically I feel like I'm 30 years old. I take great care of my body and my mind. Something I've learned recently is that after 33, I believe the body can deliver if you need it, but the real battle is mental.
"Going through many things with the focus on the end goal of staying at a high level is the hardest thing, and that's what I've been doing for the last few years. I've been working and focusing more on working on my mind. I know my body will handle me because I have a lot of respect for it and I listen to it a lot.
"Life has to have important moments, for better or for worse, but when you fall you must have the strength to get up. I'm happy, I want to stay here and see what will happen.
"I want to find out if I'm going to play until I'm 40, 41, or 42, but the most important thing is that my daily goal is to enjoy the moment."
Ronaldo is still a long way behind former United and Tottenham striker Teddy Sheringham who holds the record as the Premier League's oldest outfield player, aged 40 years and 272 days.
The official Guinness World Record for the oldest appearance in a professional, organised match belongs to Ezzeldin Bahader, who was 74 years and 125 days when he played in an Egyptian third-tier game in October 2020.
Ronaldo also hinted that soccer needs to follow in the footsteps of the NFL and NBA when it comes to giving athletes times to recover and rest.
The issue of workload has been a huge talking point, with Bayern Munich's Robert Lewandowski and Paris Saint-Germain's Kylian Mbappe speaking out against FIFA's proposal to hold the World Cup every two years.
When asked about the longevity of NFL star Tom Brady and NBA icon LeBron James, Ronaldo replied: "I think a very important point is the difference between sports.
"You mentioned some excellent athletes who have already been active for many years. In my opinion, there is no other sport that has as much workload as football. The NBA, for example, has long rest periods, but I don't want to expand on that."