Biden did not get the same medical deferment as Trump. Biden received "1-Y" classification, which meant he could only be drafted in a national emergency due to asthma as a teenager. Trump got his classification due to bone spurs, but when asked, he couldn't recall on which foot. All other deferments of both Trump and Biden were because they were students.
"I was the best baseball player in New York when I was young," Trump told interviewer Michael D'Antonio in 2014. "I was always the best at sports."
"It was a long time ago," Trump told reporters at a July 2015 campaign rally in Iowa. "I had student deferments and then ultimately had a medical deferment because of my feet. I had a bone spur."
When asked which foot had the problem, Trump – who has claimed to have "one of the greatest memories of all time" – told reporters that he could not remember."
https://www.usatoday.com/story/news/politics/onpolitics/2018/12/27/trump-vietnam-war-bone-spur-diagnosis/2420475002/
However, only 50% of people who have heel spurs actually feel any pain because of it.
“A heel spur can be an incidental finding on an X-ray. You can have one even if you don’t have heel pain,” Dr. Davis says. “When we’re treating people, we don’t focus on the spur because often the spur doesn’t have to go away for the pain to resolve,”