Angels can turn back time... but there is also the seniority factor. You must be aware that since angels can't die, they must've lived a very long time since the Beginning. Well, the negative sign represents basically what the humans call "BCE", except the human solar calendar year is not the same as the angelic year (1 angelic year = approx. 25 human years). So an angel who says he is +2 years of age is older than an angel who is -2 years old.
The response to your question earlier was obviously in angelic years.
Prove it. Or I'll assume you are referring to our mental ages in angelic years. In which case, the -15 and -1 ratio is distinctly insulting.
0 does not represent so much a year but a metamorphical stage in angelic life. One doesn't say "I'm 0 years of age", but "I'm neutral". At that stage in their lives, angels are dormant, and in some ways vulnerable, as their powers are reduced so that when they reach +1, they will increase again and emerge more controllable than they would have been at -1.