AS far as the tape coming off - if you don't get any head hair in it, it comes off really easy, and if you use the paper tape (like gauze tape) under it, it comes off REALLY easy (it won't stay long on it's own). As tough as the adhesive is, you'd be surprised how hard it is to get tape to stick on a puppy's ear! I've heard of people just using regular scotch tape, bandaids, and just about anything that is sticky. Getting the tape to stick to itself is the only way to get it to stay, really.
As far as age - 10 months isn't too old to try (you can attempt to tape ears at any age, you never know). But, once the cartilage in the ear is "set" you could tape them forever and they'll never stay up - but it's hard to know for sure when that will happen. Every Yorkie is slightly different so I would encourage you to try if you really want the ears up.
From my experience, if the ears are totally folded over at the base, you probably won't have much luck with an older puppy, but if the ears are sort-of folded in half, then the chances are good they will stand up.
Calm and collected? Haha - after you do it about 10 times, you get used to it.
Even if you have a camera pointed at your face and feel like a complete moron. LOL