If we look at historical beliefs and what has been important to Presbyterians, the invention of observances like Lent is decidedly not a Presbyterian thing; sort of like Baptists baptizing babies.
This seems like the best answer to the OP (we seem to have drifted into the general expediency of Lent), if the OP is talking about official ecclesiastical observance.
There isn't anything about historical Presbyterianism that would condemn the private celebration of Lent, though, right?
Surely private fasts are still a good thing to do -- just not sure about the forty days formulation. I've celebrated Lent before, and I think that when I did it and when
most other young Protestants do it, it is experimentation with invented traditions. On the other hand, I gave up coffee, which was a very good thing to give up; it's just that it probably would have been better if I hadn't had the gratification of feeling that I was doing something exotic and meritorious. I'm
not saying that everyone who celebrates Lent feels this way -- just noting that it could be a temptation for some.