Gonna disagree with most here- But Wogster has it about right. Your Huffy can definitely be improved on--But to what? You also have a breathing problem- that hopefully can be improved on but how far?
I have just got a couple of mates through starting to ride- One was very fit and no problems but the other was not. The unfit one had a bike equivalent to your Huffy except it was heavier -did not fit him and required a lot of Maintenance to keep running. 2 months ago he got a used Mountain bike for around $100. Big improvement on bike and it does fit. First ride out of 10 miles on the road and he was finished. Got him up to 20 miles and he was still finished. Last sunday he did 54 miles and he has sold the bike. The ride finished him----BUT- he is now looking for a road bike so he can get to the next stage of his riding. In the meantime he has borrowed a Road bike that is heavy- doesn't fit him and falls a part easily.
He still has a long way to go to get fit but he knows that he wants a road bike and not an upright one and he also realises that the little bit of cycling he has done has improved his fitness no end. He is going to make it- but not next week.
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How long was I in the army? Five foot seven.
Spike Milligan