veteran, someone who is one's senior by a significant degree

a lot / a majority

largely; mostly

an upperclassman / an older alumnus (graduate) of one’s school / a person who entered one’s workplace earlier; a senior; one who has seniority / an elder (one who is older)

experience (an experience or one's (overall) experience)

to experience

knowledge

to hold, to carry something / to have, to possess / to hold up, to maintain

holding, possession / wear, durability

continuative of 持つ