wedding - Is one suppose to engaged or married eighteen years old?

It says in Avos (5:21), "At eighteen years old לַחֻפָּה."

What does לַחֻפָּה mean? Most people translate it to mean for the [marriage] canopy, [enter] the marriage canopy or enters the wedding canopy.

Therefore, does this mean by 18 he should've been engaged? Or that at 17 he gets engaged and by his 18th birthday he should already be entering the wedding canopy?