In the following sentences below, I can't understand the part underlined well.

Past tense seems strange to me. Shouldn't it be "will keep" in the future tense?

I hope to hear your opinions. Any idea will be welcomed.

Thanks~

pb

--

A little over a year ago I began training to swim the English Channel this September. I will be
58 years old then.

(...)

One fact that contributes to my interest is that, if I succeed, I will be the oldest person ever
to swim the Channel.
I don’t think I’m a superman. I do think I have at least three things going for me:
First, I am training hard—presently swimming 7 1/2 miles a day. Prior to that time I also
kept physically fit by training moderately hard. It's past tense because he's referring to a time in the past, ie before he began training hard with his present routine of swimming 7.5 miles a day.
Second, I am a very goal-oriented person for whom this swim has long been a goal.

Best wishes, Clive

Concetrating on one thing and then can't think of others... that seemed to be the problem for me in this case.

Thanks again~

pb