I don't want to jump in when I'm not a medic but this is my view. Yes it may partly be age that makes it take longer to clear up but I also think viruses have mutated since we were younger, plus not mixing for a long time with others during lockdowns has reduced our immunity to these type of infections in my opinion. If it makes you feel better I know a lot of younger adults at work who all seem to have had some kind of cold since last Autumn that is taking ages to clear, at least 2 weeks, and often has a lingering cough.
A chest infection caused by virus or bacteria is surely catching either through breathing or touching it. Obviously some people can get over it more quickly than others.