As you get older, the physical abilities decrease, which is particularly frustrating because your brain gets so good! So as you are becoming less technically or physically able, younger dancers are emerging who need the space to perform.
You can't reduce lactic acid, but you can increase your tolerance to it. I do this through running or cycling, but it's a good idea to match your training bout to the type of dance you do.
People often argue about this. Obviously one of the skills in performance is acting, and you can't expect every Romeo to really be in love with their Juliet!