The most comprehensive study of Rembrandt's work has dated this piece as anywhere between 1645-1655 and the inclusion within this well researched documentation is enough by itself to assume that the attribution to Rembrandt is indeed accurate.
We are indebted to the Corpus Survey of Rembrandt paintings which provides us with more information on this artwork than anywhere else. Indeed, it is certainly a lesser known work that is hard to learn much about, other than it's essential details. The most recent publication in this series which is regularly updated with their latest research findings includes an image of the original work and also an adapted version that featured additional details.
It is believed that Rembrandt was painting a figure from the path, in that the armour was styled in a way that way no-longer used. The model himself would clearly have been asked to provide this thoughtful expression that helps to bring a certain level of strength to the figure. Despite his young age, there is clear confidence in his eyes. Composition-wise, it is particularly similar to Rembrandt's Pallas Athene, from the attire to the pose and the colours used.
Indeed, there is a certain level of artistic license used in the soldier's armour, mixing different ages of attire together in a way which suited his painting, but would never have been seen in reality.
The Kelvingrove Art Gallery and Museum is a relatively small museum by national or international standards, but their collection is highly impressive, containing many of the most famous artists from the Renaissance all the way up to the present day. For example, find Paul Cezanne, Pierre-Auguste Renoir, Claude Monet, Titian and Salvador Dali represented here.