Alot of astrologers don't believe cusps are ever really significant. Some think the signs kind of fade from one to the other, but others think that the first and last degrees of a sign are just as powerfull as those in the middle.
Often, people who feel that they are similar to the sign they are 'cusped' with have personal planets in that sign. If you're born in the last degrees of a sign, there's more chance your mercury had tipped over (it's always fairly close to the sun). Since mercury is the mind and communication, it can be very noticable when it's in a sign different from the sun sign. Of course, planets like venus, as well as the moon, ascendant, etc, can also have this kind of effect.
It might be interesting if you could get birth times for your friends and make them charts, so as to see where their personal planets were
Edit: without birth time and birth place, this can't be accurate at all, but on this site (
http://www.astrologyweekly.com/chart.php ), you can put in the information you do have, and it produces a chart which seems to indicate that he may, in fact, be an aries, and has mercury in aries as well. The 21st is usually the changeover date from aries to taurus.