As I've gotten older, I've gradually been becoming farsighted.
Literal
Age [object-を] accumulate [as-につれ], gradually farsighted become-coming.
年齢を重ねる ('to accumulate years') is an elegant way to say 'getting older.' ~につれ marks proportional change. だんだん + ~てきている stacks gradual change with ongoing state. 遠視 (えんし, 'farsightedness') is medical vocabulary.