Finland is not a Germanic country linguistically despite having been part of the Kingdom of Sweden for most of its recorded history until the 19th century. Over 60% of Finns belong to the Uralic haplogroup N1c1, which is concordant with the fact that Finnish language (Suomi) also belongs to the Uralic linguistic family.
One might therefore wonder whether the 28% of I1 lineages in Finland came from their Scandinavian neighbours (notably Sweden) sometime between the Bronze Age and the Middle Ages, or on the contrary whether I1 spread throughout Fennoscandia at the same time during the Mesolithic period, when the ice sheet receded over the region.
A look at the phylogenetic tree shows that the Finns, Swedes and Norwegians belong primarily to the northern cluster (L22). Out of five subclades, two (L287 and L300) are almost exclusively Finnish, while the others are Scandinavian. This is enough to think that a late Mesolithic colonisation of Fennoscandia from Denmark or southern Sweden (perhaps as late as 6000 or 7000 years ago, during the Ertebølle culture) could have brought I1 around the same time in Finland, central/northern Sweden and Norway.
This would have happened well before the first Indo-European speakers reached Scandinavia. Finland is the only country with more than 15% of I1 where the Germanic culture and language didn’t take root. A good reason for this would indeed be if Germanic culture did not yet exist in Scandinavia at the time when I1 reached Finland.
Of the 28% of I1 in Finland, 80% belong to the exclusively Finnish L287 and L300 subclades, while the rest (5%) generally resemble more closely Swedish I1. These are typically found on the west and south-west coast of Finland, where Swedes have settled in historical times and where Swedish is still spoken. This is also where most of the R1b (3.5%) and Scandinavian R1a-Z282 (3%) is to be found.
The Scandinavian I1 in Finland is found at a similar proportion to R1b and R1a as in Sweden. In contrast, Finnish I1 is found in all the country, where hardly any Germanic Y-DNA is present. This is another confirmation that the I1 in Finland is pre-Germanic, pre-Bronze Age, and consequently of Mesolithic origin.
Unfortunately this timeline seriously conflicts with the estimated age of I1a2c, which Ken Nordtvedt calculated to be only 2000 years old based on STR variatons. This method is not very accurate because it fails to take into account population size. Larger populations create more genetic variations.
Nordic countries have always had a lower population density than central of southern Europe. Before the Bronze Age, Nordic people were still hunter-gatherers, while the rest of Europe had been farming for up to 3500 years. Agricultural societies could support populations ten times higher than hunter-gatherers in similar climates.
In cold Fennoscandia, the pre-Indo-European population density must have been at least 20 times lower than in Mediterranean Europe. This means that the mutation rate would also be 20 times lower, and therefore that haplogroup I1 is much older than STR variations alone would suggest.
If the age estimate of 2000 years old happened to be correct anyway (very unlikely), the only way I1 could have become so predominant in Finland is through an unprecedented founder effect, with a single male lineage quickly replacing one fourth of all lineages in the country (a highly unrealistic scenario).