Is it true that sjogren's syndrome is more "brutal in younger patients" (under 30 yrs)?

No: Sjogren's syndrome is quite variable. It may not require any treatment, may only require "lubrication" approaches or can affect many body systems. There is no general answer. It depends what is affected.

Depends: Some younger patients (particularly under 18yo) have symptoms that can be more serious (inflammatory arthritis, rashes, affected brain, kidney disease) but it is highly variable. Most younger patients do not yet have dry eyes and dry mouth yet but they will likely develop it years later after chronic inflammation has destroyed their tear and saliva glands). Treating inflammation may prevent this.