I'm a newcomer at bonsai. I purchased a grow-from-seed kit last year while on vacation, and a year later my tree didn't grow. Should I continue trimming the lengthy leaves or wait for it to grow more? The tree is a pine plant, and it is currently 5.5 cm tall.

These kits are poor value, first it will not produce a bonsai that has to be styled if the seedling is only a year old then it will be small, it needs to. There is nothing to prune so no don not prune. It also if it is not, be outside depending how cold it is where you are, but once out never inside.

Congratulations on getting these to grow, and live and do well.

Initially it is important to get growth on seedlings and cutting the leaves is counterproductive. (When you say cut, you mean to remove leaves right? You basically never cut them to shorten the length of the needles)