Old guard and Oldtimer

Old guard noun - A faction that is unwilling to accept new ideas.

Oldtimer and old guard are semantically related In some cases you can replace term "Oldtimer" with "Old guard", this terms are similar.

Oldtimer noun - An experienced person who has been through many battles; someone who has given long service.

Old guard and oldtimer are semantically related in experienced person topic. Sometimes you can use "Old guard" instead a noun "Oldtimer", if it concerns topics such as particularly in war.