Congrats on your new Neverfull MM! I think you'll like it - the strap length will be fine!
I think I'm a few years older than you because I was around 13 or so when I went to my first concert ever (DD). Anyways, seeing DD in L.A., so unfortunately, we won't be able to meet..... I've seen DD several times when I was younger as well as now -most recently was just a few years ago when all of the original members got back together - I think I went to 3 concerts during that time frame - the best was at Staples Center in L.A. and also a small club show in San Diego (I think only about 300 people!) One of my friends who I've know since elementary school flew down to stay with me and see all three reunion concerts! She also was with me when I saw DD for the first time as a teen!! Very nostalgic!
Have a great time at the concert!! (But, don't bring your new Neverfull to the concert - got to watch out for people spilling drinks while walking around or on the floor of the concert venue!)