##tl;dr

I don't think you need spent big money on a new jacket just to go skiing if you have a serviceable soft shell.

You can wear anything you want. I know when the ski season is coming to a close some people go skiing in little more than bathing suits on warmer days, and there are competitions where people try to cross/jump over pools of ice water. I skied nearly every day in Jackson Hole, Wyoming one season and my go to jacket was a soft shell with a wind proof membrane. I chose that jacket because I would use the lifts and then hike out in the side country (out of bounds areas to the side of the patrolled areas). When I hike I tend to heat up significantly so my soft shell allowed me to dump the excess heat. I only used a regular hard shell ski jacket during the coldest of days.

In general for beginning skiers/snowboarders I'd recommend they wear something that is warm, has really good water resistance, and will keep the snow out. Hard-shell skiing jackets generally accomplish all of these things. Soft-shell jackets that I've used tend to be a bit shorter in the torso so it is easier for snow to get up underneath your jacket. Depending on how you fall and what type of snow you fall into the snow will be driven underneath your jacket. This is why some ski jackets have a "powder skirt" built into them. If you're wearing pants this is a bigger deal than if you're wearing overalls aka bibs because the snow has a better chance with pants to directly contact your skin. Keep in mind you're probably going to be falling a lot as a first timer so bigger, bulkier clothing is going to keep you warmer and cushion your falls a tad too.

The long and the short of it is I'd recommend a big hard-shell jacket, and bibs. If you're learning to snowboard and happen to have a set of hockey breezers I'd recommend you wear those too. However, anything you have, like a soft shell, that will keep you warm and dry is probably okay even if it isn't optimal. This is especially true if you are going skiing at a ski area since the lodge is close and will allow you to warm up.

As an aside don't discount the psychological benefits of a warm drink. I almost always bring a small thermos full of hot tea with me while skiing. The tea is always nice, but it is a real lifesaver when you're wet, tired, and feeling miserable.

tl;dr

I don't think you need spent big money on a new jacket just to go skiing if you have a serviceable soft shell.

You can wear anything you want. I know when the ski season is coming to a close some people go skiing in little more than bathing suits on warmer days, and there are competitions where people try to cross/jump over pools of ice water. I skied nearly every day in Jackson Hole, Wyoming one season and my go to jacket was a soft shell with a wind proof membrane. I chose that jacket because I would use the lifts and then hike out in the side country (out of bounds areas to the side of the patrolled areas). When I hike I tend to heat up significantly so my soft shell allowed me to dump the excess heat. I only used a regular hard shell ski jacket during the coldest of days.

In general for beginning skiers/snowboarders I'd recommend they wear something that is warm, has really good water resistance, and will keep the snow out. Hard-shell skiing jackets generally accomplish all of these things. Soft-shell jackets that I've used tend to be a bit shorter in the torso so it is easier for snow to get up underneath your jacket. Depending on how you fall and what type of snow you fall into the snow will be driven underneath your jacket. This is why some ski jackets have a "powder skirt" built into them. If you're wearing pants this is a bigger deal than if you're wearing overalls aka bibs because the snow has a better chance with pants to directly contact your skin. Keep in mind you're probably going to be falling a lot as a first timer so bigger, bulkier clothing is going to keep you warmer and cushion your falls a tad too.

The long and the short of it is I'd recommend a big hard-shell jacket, and bibs. If you're learning to snowboard and happen to have a set of hockey breezers I'd recommend you wear those too. However, anything you have, like a soft shell, that will keep you warm and dry is probably okay even if it isn't optimal. This is especially true if you are going skiing at a ski area since the lodge is close and will allow you to warm up.

As an aside don't discount the psychological benefits of a warm drink. I almost always bring a small thermos full of hot tea with me while skiing. The tea is always nice, but it is a real lifesaver when you're wet, tired, and feeling miserable.