Both are funny and really romantic. Fate is the theme in both. Fated to Love You will have you either laughing or crying.
Both have fate drawing the couples together. Autumn's Concerto is the best romance and the highest rated Taiwanese drama. It's more serious than Soulmate, but is a drama you will watch over and over, it gives you such a good feeling!
If you enjoy the storyline, concept, and the soundtrack in Age of Youth then you will get the same vibes and experience in Soulmate. Although the latter is made for adult and mature audience I think the concept in Age of Youth was taken from this drama. While watching this series it truly reminds me of Soulmate with awesome advise about love, dating and marriage.