ANSWER 1 : No the inferences are not completely correct. The true reason is as follows: 1. - He is always walking ahead (It talks about the times when he is walking ahead of you. At all those times, it is a continuous process. Hence it is in present continuous. the reason it is in present is because it is a habit and happens regularly even to this date); - He complains ( Since it is a habit, present simple was used. but just as the last sentence, "and is always complaining" would have been fine too); - I am too slow ( Simple present is used because 1) there is no continuous form and 2) the speaker thinks that being slow is your habit, just as simple present was used in the last sentence to show a habit or a characteristic). ANSWER 2 : It is used because it shows a characteristic or a habit. Also according to me "and is always complaining" would have done just fine too !

Your inferences are not correct. 1. ...is always doing... = a typical habit of someone that has, amongst others, an annoying effect. 2. Present simple indicates a characteristic of a person. 3. The verb "be" is not used in the continuous as a state verb.

The first two are correct, the third one isn't: - I am too slow (Present Simple is used because the sentence uses the verb 'to be' which is a state verb and cannot be used in a continuous form).