Mentions of minimum service requirements, using grenadiers à pied or equivalent as the example :
October 1796 : "grenadiers à pied de la garde constitutionelle" – 2 year prior service requirement – or – to have performed an "action d'éclat"
The other unit that was later included in the formation of the garde consulaire was the "grenadiers de la garde du corps législatif" (ex- "grenadiers-gendarmes près la représentation nationale", ex- "gendarmes de la prévôté de l'hôtel royale") – and this formation had no minimum service requirement.
March 1802 : "grenadiers à pied de la garde consulaire" – prior service of 4 campaigns – or – to have performed an "action d'éclat" – or – to have been wounded for new selectees
July 1804 : "grenadiers à pied de la garde impériale" – prior service of 5 years service including 2 campaigns for new selectees
In the decree of organization for the guard of 15 April 1806, Art. 3 it says,
"Les bataillon de vieux soldats seront composés de 4 compagnies fort de 120 hommes chaque. Les bataillons eront composés de 480 hommes chaque, et la totalité du corps de de 1920 hommes, tous soldats ayant au moins 10 ans de service dans la ligne."
This is the text as reported by Perrot & Amoudru (1821), Marco de Saint-Hilaire (1846), Fieffé & Raffet (1859) and Pigeard (1993)
Given that large numbers of prior governments' guards had been previously incoprorated (some of which had soldiers with no line experience at all), we may have to think of this requirement having application to only new selectees
Article 34 provided that a vélite (the vélites wee formed in July 1804) who made a campaign would then be admiited to the guard proper.
The creation of the 2e grenadiers (ex-hollandais) was by incorporation of pre-exisitng Dutch units in 1810, which was renamed 3e grenadiers in 1811.
The creation of the 2e grenadiers (français) was by incorporation of a prior cadre of the regiment, a draft on the fusiliers and soldiers selected from the line.
I could find no requirements for minimum prior service for these.
During the Cent Jours, per the decree of 8 April 1815 specified in Art. 46 :
For the 1e grenadiers : 12 years of service
For the 2e grenadiers : 8 years of service
For the 3e grenadier : 4 years of service, which might be assumed to apply to the 4e grenadiers formed per a decree of 9 May 1815