Getting more cautious with age is pretty normal, but it can get out of hand and paralyze you. I'm 56 and I have that in spades. My solution has been to figure out what I can do without locking up (but with a fair bit of fear), and keep doing it to desensitize myself to it. Then when it starts to get routine, push the limit a bit. Mentally you have to think of it as fun rather than as woosing out.
For your specific problem with boardslides, start with doing 50-50s then throw in a slight shiftie. Gradually increase the shiftie until you are boardsliding the second half of the box. etc.
In retrospect, "Let's get the goat drunk"
should have been my cue to leave the party.