Short answer- No. babies should not be put in a sitting / inclined position in any stroller until they are capable to sit by themselves for prolonged periods of time.

Not directly answering your question, but 2 things to consider with a 3 month old kid is - it can't fully recline the backrest and the suspension is much harder in comparison to classic "crib" style strollers. We started using it slowly at age of 6 months as (coincidentally) also recommended by Thule and as already answered by "pd", I would not recommend using it before the baby is able to sit on its own.