A lot of the reason that time seems to pass more quickly as we age is that we have fewer and fewer novel experiences; when each day resembles the one before it, whole months can disappear in lived monotony.

I like to think of memory as using a sort of compression algorithm. Repeated data gets compressed away; novel data takes up space.

So you can slow down your time perception by making your life less compressible. Do things differently; make bigger changes in your life more often; make more milestones; take more trips; change things up; be random.