When I first started Kenpo, I was 13- still had a lot of energy, flexibility from gymastics.......so really the hardest thing for me was remembering all the new technique names.
I still do Kenpo twice a week now......but have just started another new school on alternating days......also two days a week. I am now 32, have old Kenpo injuries against me, not as energetic as I used to be........and am in class with a bunch of teens!! So now the hard part is trying to keep up with the cardio. they do in this new class, trying to learn something new and not pop into my Kenpo stuff right in the middle of a new technique and remembering the new names for things.
Also, I wear a white belt for this new class and honestly, don't get a whole lot of respect from the teens.......like I do in Kenpo where I am a higher rank. Maybe it has nothing to do with rank, maybe they just don't respect new people......but that has really changed since I started Kenpo back when I was a teen......everyone was respectful, regardless of rank.