Nacer would not normally be used in the imperfect because it means to be born. That only happens once and it is a completed past action. That would more than likely be used in the preterite. The imperfect is used to talk about habitual past actions, describe what something was like, or to express a continuing past action.(Something that went on over a non-specified period of time.) The preterite has a definite past time expression either expressed or implied, whereas the imperfect may include a general past time expression.
Yo nací hace veinte años. I was born 20 years ago.
When you talk about how old someone was, generally you would use the imperfect because the age went on for a year. Ella tenía 5 años. It gives the setting to the story that you are telling.
The past participle of ir is ido and it would be used with a form of haber to form the present perfect.
The present participle of ir is yendo and is used with a form of estar to form the present progressive.
Here is a link to the verb conjugator that can be found in the "lessons."