I would say: I am slightly taller than he is. I'm not nearly as tall as he is. I'm nowhere near as tall as he is. If you want them all to have the same meaning, the first sentence would have to be,"He is slightly taller than I am." the sentences in the second set both express the same thought. I studied Japanese for one year. I have studied Japanese for one year. Both are pretty much the same, although in the first sentence I would be thinking about a completed action and in the second about a completed process.