I've started using the interval ear trainer online and I can't seem to distinguish minor 6ths, major 6ths, minor 7ths and major 7ths from each other. When I hear them they all seem to sound alike to me. It's very frustrating and I haven't improved much. Any tips?
for major 7ths i always hear the need for it to resolve up. also, try attaching an a jingle to each interval. For example the three note "NBC" jingle is up a major 6th and then down a major 3rd
i could play like eric clapton if i had his gear...anyone could
If you do them one directly after the other, you can tell a difference though? IE Play a major 6th, then a minor 6th, you know they sound different?
If so, I think it'll just come with time. Practice playing them on guitar/ other instrument, and try and work them into a melody.
It's usually easiest to identify intervals by associating them with songs. So whenever you hear two notes that sound like the beginning of Smoke on the Water, you will know that the interval is a minor 3rd.

This site has a lot of songs that you can choose to identify intervals with, just choose and interval and then choose a song you are most familiar with. http://www.people.vcu.edu/~bhammel/theory/resources/macgamut_theory/songs_interval_recognize.html
Practice trying to sing the intervals. Singing intervals can help you hear them better.
I also suggest singing the intervals, I've never done anything even remotely connected to music until I was 17 and nobody in my family was in music, so I really had no predispositions for having a good ear. I started noticing improvements when I started singing along to the music I hear on radio. Then I tried to play some tones on guitar and tried to sing them. Eventually, my hearing got better so now I can transcribe most of the songs I listen to by ear.