Complex sentence: Since his father was known to have died in the year 900, Malcolm must have been born no later than 901, by the 940s he was no longer a young man, and may have become impatient in awaiting the throne.
Split into simpler sentences: Since his father was known to have died in the year 900, Malcolm must have been born no later than 901. By the 940s, he was no longer a young man, and may have become impatient in awaiting the throne.