Q. This question is not exactly about Islam, but rather the occupation
of Prophet Mohammad [PBUH] before he got Risalat.

A. Note that the definition of Sunna according to the hadith scholars
(unlike those of fiqh and usul al-fiqh) is: All that is reported from
or about the Prophet _both before and after_ he received prophethood.
For more details see my recent post "[1] The meaning of Sunna" on SRI.

Q. When did he started travelling with trade caravans?

A. The earliest time on record -- and Allah knows best -- seems to be age
twelve went he went to Sham with Abu Talib as narrated by Ibn Sa`d in
his Tabaqat and Ibn `Asakir in Tarikh Dimashq, also al-Tirmidhi who
graded this report fair (hasan). At that time a monk or several
Christian monks -- Bahira in some reports, Sergius in others -- told
Abu Talib that his nephew would be a prophet. Abu Talib alludes to
these incidents in some verses of poetry that we have from him:

    The people did not return until they had seen, pertaining to
    Events that cast light on every heart,
    Nor until they saw the monks of every town
    Prostrating to him in groups and individually.

Subsequent hadith masters such as al-Dimyati and Ibn Hajar said that
al-Tirmidhi's report incorrectly includes Bilal in that caravan.

"Sham" includes present-day Syria, Palestine, Lebanon, and Jordan.

A trip to Yemen took place between 11-19 years of age. Ibn al-Jawzi
relates in al-Wafa bi Akhbar al-Mustafa that at that time he went to
Yemen with his uncle al-Zubayr ibn `Abd al-Muttalib.

A second trip to Sham took place at age fifteen according to Ibn
Ishaq, Ibn Sa`d, Ibn al-Sakan, Abu Nu`aym and others. At that time Abu
Talib sent him in representative partnership of lady Khadija's
interests and remained behind, while Khadija sent her servant Maysara
with him, and Ibn Sa`d narrates that Abu Bakr went also. Maysara
reported more signs that he saw pertaining to prophethood, including
another announcement of his forthcoming prophethood by the monk
Nestorius. Khadija later told her cousin Waraqa ibn Nawfal about this.
Ibn Ishaq relates the following poetry from Waraqa:

    I believe that he shall soon be sent as a truthful herald
    As were sent the two servants, Hud and Salih.

The age of the Prophet -- Allah bless and greet him -- at the time he
married Khadija was 25 according to the vast majority of scholars. She
was 40.

Q. What type of products he carried from Mecca, What he brought back?

A. This is not mentioned in the reports and Allah knows best. The reports
only mention Khadija's "property" (mal, amwal) and the Prophet's
selling -- Allah bless and greet him -- and buying "commoditiy"

Q. Which trading routes he actually used: Did he went as far as Yemen OR Jordan OR Iraq OR Syria?

A. Yemen and Sham as we said.

Q. How long it used to take to make a typical trip?

A. At least two months to Sham. When the Prophet -- Allah bless and greet
him -- came told the Quraysh about his Isra' to al-Qudus, al-Mut`im
ibn `Adi (he died an unbeliever) said: “We strike the flanks of the
she-camels for one month to reach the Hallowed House, then for another
month to come back, and you claim that you went there in one night!”

Q. How many trips he made through out his trading occupation? How many times he made the trip on behalf of hazrat Khadija?

A. On record I found only the three mentioned above, the last one on her
behalf, but he must have made many more trips between then and age
forty, at which time began the tremendous matter of Prophethood, and
Allah knows best.

GF Haddad