If you want to aak the opposite of 'how long ago', for example how long ago did you graduate from college, you could ask 'how much longer' (ex: question: 'How much longer until you graduate from college?' Answer: 'two more years' or 'I'll graduate in two more years.' )

Both are correct but have different usage. "How long from now" always refers to a time interval. Ex: "How long from now will you graduate from university?" You could also simply say "When will you graduate from university?" An answer might be 2 months, 1 year, etc... "How far ahead" always refers to distance. Ex: Think of a situation where you and your friends are driving two separate cars to get somewhere. "My friend started driving an hour ago! How far ahead do you think he is?" And the answer would be some distance, ex: 50 miles. The antonym for how far ahead is "how far behind".